When I first started out fishkeeping, I'll admit I was a bit of a scaredy cat. I was already a little bit nervous around the fish, let alone the much smaller organisms living around the tank - and it turns out, there's a lot of different kinds of six, eight and no-legged creepy crawlies that can inhabit our aquariums. The good news is, the vast majority of these aren't going to do any harm to you or your fish.


Whilst it'd be ideal to sort these bugs based on how they look (such as how many legs they have), some invertebrates can be too small to see clearly with the naked eye - and if you're anything like me with phone cameras, they seem to become more blurry once they're photographed! The way we're going to sort these guys out is by figuring out what part of the tank they're living in. Most of the invertebrates have a specific niche, or a way of living, that can be identified with a bit of observation. For example, your classic snail might live mostly on the glass, or it might live under the gravel.


red brown ramshorn snails

Above: Red and Brown Ramshorn Snails.


In and Around the Substrate

If you've ever looked at the gravel or sand in your tank, it might be moving a little. Of course some burying fish may do this, but sometimes it's something a bit smaller and creepier. More often than not it'll be Malaysian Trumpet Snails, which are often found turning over the sand and munching on spare food. 


Tubifex and Blackworms

Commonly used as a live food source for fish, on the rare occasion you might find Tubifex or Blackworms in your aquarium. Typically these get eaten up pretty quickly, so they aren't often found unless you've introduced them specifically. Tubifex worms belong to the Tubifex genus (as the name might suggest), while Blackworms belong to the Lumbriculus genus. Despite being in different families, both of these worms look similar - they tend to be reddish-black in colour, a few millimetres in diameter and range from 5 to 15cm in length. Lumbriculus tends to be shorter and thicker, and "swim away" if disturbed, while Tubifex tend to be long and thin, and will "retreat" into the substrate when disturbed.


Both of these species like to live in the substrate (whether that's mud, pebbles, sand or just debris) and will often be seen either digging around looking for food or staying in one spot, half in the substrate and half dancing (or just sitting around) in the water column. Despite being a little bit creepy and a little bit prickly looking, both of these guys are harmless to fish and will usually be eaten by fish.


It's worth noting, however, that Lumbriculus tends to be the preferred species to culture for fish food, as Tubifex can be known for being a host for internal parasites.

tubifex and blackworm

Above: A good food source, the left is believed to be Tubifex tubifex and the right is believed to be Lumbriculus variegatus.


Detritus Worms

It's a bit hard to give an exact explanation of what counts as a Detritus worm, but the many 5-10mm white squiggles can be almost impossible to identify with the naked eye regardless (to add to the confusion, Tubifex may sometimes also be referred to as Detritus worms). Detritus worms pretty spiky looking, but are non-parasitic, and usually enjoy feeding on, as their name implies, detritus (basically, dead stuff and poop). They can be found in the substrate behaving much like the above Tubifex and Blackworms, but can also be found on the glass and even on the surface.


An over-abundance of these may be a sign that your tank is too high in stocking or you may be overfeeding, but overall these bugs are harmless for your fish (and may even make for a good snack). 


Above: Both of these may be called Detritus worms by fishkeepers. Left is believed to be Stylaria and right is believed to be of the Aeolosomatidae family.


Malaysian Trumpet Snails

Fortunately, Malaysian Trumpet Snails (MTS) are pretty easy to identify - but unfortunately, they can also come in pretty big numbers. However, other than their large population size and looking unsightly to some, Malaysian Trumpet Snails are both harmless and can even be desirable. Some fish such as large loaches enjoy feeding on MTS, and the snails themselves can also be useful for turning over the substrate in your tank.


An interesting fact about Malaysian Trumpets is that almost all of those found in the aquarium are likely to be female! MTS are livebearing (and thus don't lay eggs), however only the females can reproduce asexually (have offspring without a male).

malaysian trumpet snail

Above: A young Malaysian Trumpet Snail.



Amphipods are pretty unusual in the aquarium as (like Tubifex and Blackworms) they make for easy snacks for fish, however we've included them as they're almost kind of cute! Amphipods are small, shrimp-like crustaceans that you may find "scooting" or "hopping" along your substrate. It's possible large ones may eat fry, but otherwise Amphipods are harmless to your fish.


Above: A marine Amphipod species. Photo © Hans Hillewaert / , via Wikimedia Commons



On The Glass

Have you ever checked out your tank a few hours after the lights were off? You might notice a few different types of creepy crawlies that prefer slightly dimmer conditions, such as snails.


Other Snails

Probably the most common "pest" found in aquariums, you can read all about snails here. Easy to identify, snails are a "love 'em or hate 'em" kind of thing. As they are harmless, I personally appreciate the hard work that snails put in feeding on debris and leftover food - they also make great food for fish like loaches and puffers. Common snails include Brown Ramshorns, Pond Snails, Bladder Snails, and the Malaysian Trumpet Snail introduced above.

ramshorn pond snails

Above: A Brown Ramshorn Snail (left) and a Ladder Snail (right).



Although they aren't technically true Limpets, what we call Limpets in aquaria look a little bit like a snail with a hat (instead of a twisting shell). Limpets tend to only reach a few mm in length, make good snacks for fish and may be more visible at night - they are also harmless (and, in my opinion, pretty cute!).

freshwater limpet

Above: A freshwater Limpet.



Now, Planaria (a type of Flatworm) do tend to get a few people freaked out, however these guys aren't usually as scary as they seem. Flat in appearance (hence their name) with a characteristic arrow-shaped head (if large enough to see), Flatworms are almost always harmless to fish and are generally more unsightly than anything. Large Flatworms may predate on fry, however this is not common and their populations can be controlled by preventing overfeeding and overstocking.


Above: A Flatworm species, Photo By Eduard Solà (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons



Okay, so with these guys a little bit of nervousness is warranted. Hydra are pretty fascinating organisms but they do have a downside - the end of those tentacles are capable of stinging. The first thing to note is that there are several kinds of Hydra, which typically present in two forms: The first are larger and white, which are the slightly worrisome kind. The second are smaller and green, and are a bit more harmless and tend to feed on Daphnia and Brine Shrimp (in fact, the ones photographed below were found in a tank being used to raise Corydoras sterbai fry without any casualties). Interestingly, the green Hydra have a mutualistic relationship with single-celled photosynthetic algae Chlorella, which may be why they tend to be less predatory towards fish.


The second thing to note is that generally, the larger white variety aren't too much to worry about - these guys aren't going to take down a tank of fish! They have, however, been caught occasionally sneaking fish fry. Hydra can be a bit difficult to eradicate from a tank and may sometimes go away on their own (as larger fish enjoy eating them, despite the stringers). The best methods appear to be creating a slightly salty tank, syringing salt straight onto them (this seems to be the most effective method) or getting a fish that eats them (such as Blue Spot Gourami, Trichopodus trichopterus, however we recommend fully researching any fish before purchase). Some say that Praziquantel may eradicate Hydra, although in the experience of myself and some others, it was not successful in affecting their populations at all.

green photosynthetic hydra

Above: Green, photosynthetic Hydra.



Above The Water

Those that live above or on top of the water tend to be too small to identify, and are often seen hopping around on stagnant water. There's usually two possible creepy crawlies that live here - Mites and Springtails.



Mites are part of the Arachnid class, and sometimes things with eight legs can sound a little scary - fortunately, Mites living on the surface of your tank are both very small and very harmless. They can be hard to identify with the naked eye, and can be mistaken for Springtails or even tiny, bouncy specks of dust. If you find Mites a little unsightly or creepy, one way to reduce their numbers is to increase the water flow at the top of your your tank, creating surface agitation that these little guys aren't too fond of. Otherwise, they serve a bit of a purpose as free fish food for top-dwelling fish.

mites microscopic

Above: Aquatic Mite. These guys are so small they're best viewed under a microscope!



Springtails are the Mites' 6-legged friend. They can be found bouncing around on the surface of your tank water, although they've even been found living in cansiter filters. Like Mites, they are small and harmless, and are also a source of food for fish. To reduce their numbers, you can try increasing surface agitation, or preventing overfeeding.

aquatic springtails

Above: A species of aquatic Springtail. Photo by Christian Fischer [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons



Bugs Not Covered


pond snail eggs

Above: Some Pond Snail eggs forming in a jelly-like sac. Almost so ugly, they're cute!


Aquatic invertebrates are incredibly diverse, making it tricky to cover every different kind of bug out there. If you didn't find what you're looking for above, feel free to check out our Gallery for more photos of inverts that can be found in the aquarium. Alternatively, our Contact Us is always open, where we're happy to try to help with identification (although we can't promise anything)!



When you see the little black tufts of Black Brush Algae (BBA), the colour “red” doesn’t really come to mind - however, these algaes belong to a group called the Red Algaes or Rhodophyta. Red Algaes are a little bit different in nature to Green Algae, especially in their “Niche” or the environments they’re evolved to live in.


 black brush algae bba



What Makes it Thrive?

Red Algaes typically live in Marine environments, however there’s a few types commonly found in our Freshwater aquariums. The most common of these would be the Black Brush/Beard Algae mentioned above, but less commonly found is also Black Staghorn Algae

Black Brush Algae is easily recognizable, and is much like its name. It typically appears as small black (sometimes with a green, blue or red tint) tufts that attach to driftwood, rocks, ornaments, glass, and more frustratingly - plants. Black Staghorn is similar in colour, but has an appearance almost like cotton or iron wool. Both of these algaes are harmless, but can be difficult to tolerate when they begin to out-compete our beloved aquatic plants, or when they clog up filter outlets such as spray bars. 


black brush algae driftwood

Above: Black Brush Algae


The good news is that if you don't have live plants, or the algae doesn't appear “out of control”, it's a normal part of a healthy ecosystem. Red Algaes are special - you could even say they're a positive sign of a healthy tank. 

Red Algaes are found under different conditions to most other Algaes (which are often seen as a sign of an unhealthy tank). Some conditions known for thriving Red Algae may include:

- High flow. 
- High Oxygen levels.  
- Low light (you heard me right!). 
- Clean, unpolluted waters. 


Of course, as with any ecosystem, algae can mean something is out of balance, but this is mostly important if you would prefer plants to take its place in the tank. For example, Red Algae can be found at greater depths than other types of Algae - this is because in deep water it predominantly absorbs the Blue spectrum over other colours (Blue being a colour that penetrates water better than other colours). This means that lowering your lighting levels/hours may not help significantly, but if you have excess Blue light (such as using Marine LEDs on a Freshwater tank), these may be increasing the growth of your Red Algae. 


rhodophyta wavelength

Above: Rough graph of the absorption spectrum of some pigments found in Rhodophyta species.


A key factor is Oxygen levels - this may indicate a lack of CO2. This is absolutely perfect for most fish (provided they appreciate the flow), but it may not be an ideal situation for plants. This brings us to the best ways of how to combat this kind of algae. 



Combating Red Algaes

As mentioned above, these steps may only be necessary for planted tanks. Algae is a natural part of most aquatic ecosystems. It provides food for fish, it helps to remove Nitrates, it can even provide places for fry to hide amongst. But we certainly empathize with those trying to grow plants instead of algae!



Simply adjusting your tank’s conditions can help prevent the growth of this algae. One way is to reduce the flow, reducing the amount of Oxygen getting into the tank. It is, however, incredibly important to maintain some surface agitation to keep adequate Oxygen levels for your fish. 

Algae Eaters. There, we finally got to the solution many would like to jump to. Unfortunately, few fish are actually known to eat this kind of algae, and they tend to have specialized needs in the Aquarium. We’ll explain the needs of the recommended fish at the end of this article. 

Although it may not help if your lighting is normal, if you do happen to have excess Blue light, it may be worth reducing its output. 



Seachem's Flourish Excel (this really deserves a section of its own) - the product known for killing this algae for several reasons. Firstly, the active ingredient (Glutaraldehyde) is used as a sterilizing agent and it, well, kills. Excel is perfectly safe for fish when following instructions, and it is generally safe for most fish when double (or even triple) dosed - however it can be deadly on sensitive fish. 

Double dosing may not be required in most cases, as there's a more efficient method of going straight to the source. Turning any flow off and syringing (or using a pipette) the Excel directly onto the affected areas is generally a highly efficient method of killing Red Algae. When the water levels are lowered, a paintbrush dipped in Excel can be used over the ornaments, glass, rocks and driftwood and will often kill the algae on the first go. However, painting Excel isn't recommended for plants - it'll melt them! 

The other reason for Excel's efficiency is that it creates an environment in which plants thrive and out-compete the algae. This also means it's a bit of a long-term solution, as algae can bounce straight back when the treatment is stopped, and the plants lose that environment in which they were thriving. 

H2O2. You know that joke about the man who asks for H2O, too? Well in this case, it's actually beneficial. A 3% solution dosed at 0.3-1.0mL per Litre (3-10mL per 10 Litres) directly onto the affected areas can quickly reduce Red Algaes (and may even work on other types of algae), however this is a bit of a band-aid solution. When dosing, it’s important to turn the filters off, make sure fish aren’t in the way and to reduce the dosage in tanks with sensitive fish. Some also like to perform a 20-50% water change after dosing with H2O2, although this dissipates fairly quickly anyway.

CO2. This is the ultimate, long-term method for preventing both Red Algaes and other kinds of Algae. CO2 (along with additional nutrients/fertilizers) creates an ideal environment for plant growth, which allows for plants to outcompete all kinds of algae. Choosing the best form of CO2 for your tank is a whole other topic, however a common method is through CO2 injection, which requires the use of a CO2 Canister, Regulator and several other pieces of equipment. The addition of CO2 typically accompanies high lighting and nutrient dosing, and puts the tank into the category of “High Tech” - although a “High Tech” tank can be successfully done with DIY methods and may not require high maintenance. CO2 can seem a little bit intimidating at first (and it is important to do it correctly), but it is well worth it when wanting healthy, colourful plant growth in your aquarium.

Dosing items before they enter your aquarium can be helpful, such as dosing waterlogged driftwood, or aquatic plants in a stronger solution than those above. However, some feel this isn’t particularly effective, as BBA can be carried through all sources of aquarium water (and can easily be in the same water as the fish you take home from the store).



Scrub, scrub, scrub. After a while of trying to remove BBA, sometimes it’s easiest to just remove the major ornaments and to use some elbow-grease to remove all of the algae. Using a scraper (or even an old credit card) against the glass will usually easily remove the algae, which can then be picked up with a siphon during a water change.


Black Staghorn Algae dying

Above: Dying Black Staghorn Algae on driftwood.



So, What About Those Algae Eaters?

The main fish known for eating Red Algae is the Siamese Algae Eater (Crossocheilus spp., “SAE”), which unfortunately is a name that can cover several different species. Truth is, they’re not easy to identify, and many “false” SAEs can be available also. Fortunately, it seems most of the fish available in New Zealand labelled under this name appear to eat the Red Algaes they’re intended to consume. 


Siamese Algae Eaters have two main differences to take note of:

- Unlike some algae eaters like Bristlenoses, the SAE does best (in our opinion) in groups. I personally have no doubt that these fish do great in groups, and can become aggressive when kept alone. Some notice this fish likes to pick on larger (or smaller) fish such as Angelfish, however this behaviour often reduces as the group size of SAE gets bigger. These fish show some wonderful “fluttering” behaviours in groups - it almost feels like keeping a pod of dolphins sometimes!
- These fish can get pretty large. It seems, possibly due to a range of species being available, that the final size of SAE varies a bit - but even the smallest fish can be quite large to many fishkeepers’ standards. I wouldn’t recommend keeping a group of these fish in a tank under 300L in size.


As with all other kinds of algae eaters, these fish still need to be supplemented other foods in their diet alongside the algae growth they’ll (hopefully!) decimate. 


Siamese Algae Eaters Crossocheilus 

Above: Two Siamese Algae Eaters (Crosscheilus sp.)


Distribution Temperament and Compatibility Temperament Towards Conspecifics Social Behaviours Diet
Southeast Asia Peaceful/Semi-Aggressive Peaceful Social in Nature Herbivorous
Minimum Tank Size pH GH Temperature (Degrees C) Max Size (cm)
300L 6.0-7.5 1-15 20-27 7.0-15.0



Two other fish known for eating Black Brush Algae include the American Flag Fish (Jordanella floridae) and the common Molly fish (Poecilia sphenops), however people’s experiences seem to differ with these fish. I have personally kept American Flag Fish which haven’t touched my BBA, but others swear by them. These are both wonderful fish to keep regardless of whether they may eat algae, and also require research before purchasing. 




Black Brush Algae can often be seen as a fishkeeper’s nightmare, but it doesn’t have to be. The key to reducing the growth of this algae is to create an environment in which it doesn’t thrive (and is out-competed by plant growth), which can be a tricky task but is truly rewarding when you get to see the resulting lush plant growth. 

Have any questions or suggestions? Feel free to Contact Us! 






Snails in Fishtank

DSC 4993

Above: Brown Ramshorn snail front, Red Ramshorn snail back. And some dirty glass!

OK, so some snails hitched a ride on some plants you got from the local pet store, and before you know it, they're everywhere! You're now worried; Will they eat my plants? Will they add to the extra bioload? How do I get rid of these things?

Scroll down to the bottom if you simply want to get rid of them!

An important thing to consider is that snails aren't all bad! Many fishkeepers let these little "pests" live happily in their tank and don't go to great lengths to remove them. Snails have loads of benefits - they're great cleanup-crew (meaning they will happily eat any leftover food or decaying fish in the tank) and they make for awesome fishfood, along with a good indicator as to whether you're overfeeding or have a dead fish hidden away somewhere!

Will they eat my plants? In my experience, no. I have brown Ramshorns, Malaysian Trumpet Snails (MTS) and Bladder Snails and none will chew on my plants. My only annoyance is with MTS, which will dig up sand and gravel and thus dig up delicate plants like dwarf hairgrass.

Do they add to my bioload? Once again my answer is no! Snails are actually a pretty good indicator of your bioload and feeding - they will only boom in large numbers if you're feeding too much, and if they weren't there it would just be food rotting away (and even fungusing)! If you feed very little, you're unlikely to see many snails in the tank. As said above, they can be a good way to tell if a fish has died as you'll see them all gathering in one area.

The three main types of pest snails we get here in NZ are Pond snails, Ramshorn snails and Malaysian Trumpet Snails. People also often keep Mystery Snails and Apple Snails as pets.

Malaysian Trumpet Snails (MTS)

DSC 5003

Above: Young Malaysian Trumpet Snail

MTS are very commonly found in planted tanks at fish stores. The majority of MTS you will see are female, as unlike other snails the MTS is either female or male, however only females may reproduce asexually.

MTS are very useful in tanks with fine gravel and sand as they are constantly digging through the substrate and airing it out, which helps to decrease the chance of "gas pockets" forming under the substrate. You'll likely only see a few out at day as they are nocturnal, but when you look at night they can seem to be everywhere!

MTS are livebearers, so you won't be able to find any eggs of theirs!

I have found the only downfalls of MTS are that they will uproot delicate plants and smaller fish such as dwarf puffers will not eat them.

Bladder/Pond Snails

DSC 5993

Above: Bladder Snail

Bladder snails are about 6-9mm and are quick to reproduce. These guys are my favourites as they are easy for other fish to eat, are large and easy to pick out and will even happily eat some kinds of algae! Bladder snails lay their eggs in thick blobs which can be easy to remove, but some fish will even happily eat these!

Some say that pond snails will eat plants, so take that as a word of caution, but in my experience they have left my plants alone.

Ramshorn Snails

DSC 4988

Above: Red Ramshorn snail front, Brown Ramshorn snail back

Brown ramshorn snails are the smallest of the lot, topping at about 3mm in size! Red ramshorn snails can get slightly bigger, however. Ramshorns were my first snails to be introduced into my tank, and I have no regrets keeping them! These guys are excellent at eating spare food, and larger fish will happily pick away at them.

Ramshorn snails also lay their eggs in the gelatinous blobs just like pond snails, however I have found them far too small to see!

But I'm still not happy with them, and I want them gone!

You have few options when getting rid of snails, especially for those in small tanks. Many people find a reduction in snails when using some methods, but don't often find them to completely disappear.

- Copper "Snail rid": This is my least recommended method, but will work on a tank with no fish or invertebrates. It will also work on a tank with only fish, however in some water conditions (eg in certain water hardnesses) it can be dangerous towards fish. However, I sometimes use this on plants before putting them in the tank.

The copper in "Snail rid" will kill off all snails, but be careful as it will also kill off other creatures like shrimp!

- Squishing them! Many use this as a good form of snail control - they squish whatever snails they see along with any eggs. Often, people will create a "snail trap" or simply put some lettuce at the top of the tank overnight and remove it in the morning just before the lights turn on - during the time that it's in there, loads of snails will have gathered to chew on your vegetable of choice, thus making them easy to remove! This is probably my recommended method.

- Fishy snail control: This I would only recommend in tanks large enough for the fish in question. Many loaches (Clown, Yoyo, Dwarf Chain etc) will happily decimate your snail population, but a lot of these fish require tanks over 150 litres! Clown loaches, the biggest of them all, need tanks of 400L and can live up to 50 years! The vast majority of "snail eating" loaches require schools, so be prepared to have a school of 6+ as they can easily become lethargic and depressed on their own. I would only recommend this option if you have done full research on your desired fish and are prepared to look after them for their full lives!

Some would recommend puffer fish such as the Dwarf Puffer, however puffers are very aggressive and may only be able to live in the tank for a short amount of time (if at all!). After it has "done its job", you will need a tank of at least 21L and will in fact need to continue to grow snails to feed it as its staple diet! So obviously these are not a good option for a quick fix!

Have more methods or better experience with snails? Feel free to leave a comment on this article!

Tank Pest

One of the most common questions is “How do I get rid of this gross stuff in my tank?” and it’s a pretty important one, too. However, the first step to eliminate algae is to identify what it is that’s plaguing your tank. Different kinds of algae (such as red algae, green algae, diatoms and the infamous Cyanobacteria, which isn’t even an algae) all thrive in different conditions. For example, Cyanobacteria thrives in areas of low water movement and is often found on glass and substrate, whereas Black brush algae (a red algae, also known as BBA) thrives in areas of high water movement and is often found on equipment such as spray bars. Some algae like Green Water (Infusoria) and Cyanobacteria can easily be wiped out with a change of lighting such as 3 day blackout, but others can be more finicky and respond better to a change of nutrients such as BBA or black Staghorn algae which can be killed with a CO2 treatment. This is why it’s necessary to determine what you have, as reducing light won’t affect BBA and adding CO2 won’t affect Infusoria.


Two good things to note:

Almost all algae types can be reduced with the use of plants. A lot of algae thrive on excess of one thing in particular. While it’s important to fix this excess (not doing so will continue the growth of algae), using fast-growing plants can help to use up the nutrients that the algae would otherwise be feeding on. Good plants for this job are mosses, stem plants such as Hygrophila polysperma and Ambulia, and emersed plants which grow simply with their roots in the tank such as Lettuces or common houseplants. You’ll typically find algae thrives on the leaves and stems of slow growing plants such as Anubias, Echinodorus species and Java ferns, which makes them less useful for the quick job but help to use up nutrients in the long term. Plants have the added benefit for using waste nutrients such as Nitrates and Phosphates, which can only otherwise be removed through denitrifying bacteria, chemical filtration or the usual process of water changes. These plants will not only help to out compete your algae, but add to the overall health of the tank and are incredibly beneficial.

Algae is normal! It’s difficult to find a tank without a spot of algae. There’s no problem with the occasional bit of Green Spot on your glass, or some BBA on the spray bar. It becomes an issue when that BBA starts to spread and engulf your ornaments, plants and everything else! An excess of algae means that there is an imbalance in the tank and with some such as Nitrate-loving types this can be a dangerous sign. When this happens, it’s important to start fixing the balance so that either few nutrients are present, or your plants can begin to out-compete the offending algae types. In the wild, however, certain algae types are very natural and even help to provide food and shelter for fish – for example, it’s highly important for your algae-loving suckerfish! Fish such as Otocinclus sp can struggle in the tank when no algae is present, as in the wild they would have an important relationship with these algae types. The only “algae” not eaten by fish is Cyanobacteria, which also often gets out of control fast and is important to fix when it shows up.

Below are three infographics designed to give you a simple overview of the common algae types and the typical treatments used to reduce them. Under these images are linked articles which will be added over time for more specific views on how to reduce certain algae types. If you know of more reliable treatments or information on different types of algae, feel free to let us know via the Contact Us or forums!

Algae Types infographic

Algae Types infographic

Algae types infographic


Specific Algae Types:

Algae Profile: Green Algae

Algae Profile: Cyanobacteria

Brown Diatoms: Coming Soon

Red Algae: Coming Soon


The first thing you’ll likely have learned about Cyanobacteria (“Cyano”) is that it is not an algae, but is instead a type of bacteria. This means that most algaecides won’t kill it, and that it has a specific niche where it can inhabit certain environments.



Some basic facts about Cyanobacteria and things to remember:

  • There are several different strains of Cyano, with each strain having different arrangements of cells such as the common filamentous strain (Oscillatoria) to the unusual rectangular colonies formed by Merismopedia Cyanobacteria.

  • Cyanobacteria are photosynthetic, meaning it relies on light to live. They use Chlorophyll A, Phycocyanin (which gives it the classic blue-green tint) and some Phycoerythrin. The absorption wavelengths for these are given below, however it is important to note that Cyano thrives on green-yellow light.

  • Cyanobacteria are anaerobic, this means that they thrive in areas with low flow and thus low oxygen.

  • Colonies can double in size within a day’s time as they spread very quickly. This means that while quick methods such as algae killers and antibiotics (particularly erythromycin) may be suggested, Cyano can quickly bounce back after treatment has finished. This makes it essential to treat the cause, rather than to use “band-aid” solutions.


filamentous cyanobacteria

Above: Filamentous Cyanobacteria


  • No freshwater fish will eat Cyanobacteria. It’s also important to remember that while fish may eat certain types of algae, the addition of them adds to your bioload and overall nutrients, which can further feed other types of algae.

  • Like algae, Cyanobacteria requires nutrients to survive. A heavy infestation of Cyano may indicate a too high a bioload, or too few water changes.

  • The death of a large portion of Cyano can lead to a sudden increase in nutrients (such as Nitrates) in the tank. It’s important to keep up water changes to prevent nutrients from rising too high. Make sure that your filter is large and healthy enough to deal with the increase of Ammonia, or an Ammonia or Nitrite spike may develop.

  • Changing one variable at a time may be preferable to allow for you to figure out what the general cause is. Changing too many variables at once may lead to confusion and even outbreaks of other kinds of algae.


Cyanobacteria Wavelength

Above: Some of the wavelengths of light which Cyano may absorb.


Here are several steps that can be taken to reduce the growth of Cyanobacteria:

  1. Water changes, water changes, water changes. Cyano will be thriving on the amount of nutrients and organic build-up in the tank. The death of Cyano will also increase these nutrients, and water changes are the most efficient way to remove the excess. It is also very useful to physically remove the Cyano which will easily collect in the siphon, making water changes even more important for the reduction of Cyanobacteria.

  2. Lighting is very important and has many factors. The first factor is lighting hours. Often, it’s not necessary for lights to stay on longer than 8 hours a day - even 5-6 hours may be preferable. Try to keep your lighting hours within the hours of the ambient light around your tanks to prevent the overall lighting from being on for too long.

  3. Lighting quality is the second factor. As mentioned above, Cyanobacteria thrives in green-yellow light, which plants need very little of. Poor quality lights are high in the green spectrum due to green being the brightest colour. Good quality lights may look no brighter, due to the lack of green-yellow, however they are typically better for plant health and reduce undesirable algae growth. It is also preferable to check the recommended replacement time for your lighting, as some lights (such as Fluorescents) change their spectrum as they age and may need changing every 6-12 months.

  4. Ambient light can have a significant effect on what happens in your tank. Direct sunlight, especially during summer, will grow all sorts of algae along with Cyano. For tanks with a lot of sunlight, it may be worth blacking out the back and sides of the tank. For tanks outside, covering the tank during day time may even be necessary.

  5. Increasing water flow and surface agitation can be used to increase the oxygen levels in your tank. As mentioned above, Cyano thrives in areas of low flow and low oxygen. Low oxygen levels can cause problems in many fish, however be sure to not increase the flow higher than what is comfortable for your fish. Fish such as Gourami and other air-breathers are adapted to low-flow environments and may struggle if the flow is increased.

  6. Nutrient levels are a big problem. While water changes are often the first step to reducing these, other methods may include using Chemical media, reducing your bioload, and using plants. Plants are very useful in tanks for so many different reasons, but especially for reducing nutrient levels. Without anything removing nutrients from the tank, there is nothing to out-compete organisms such as Cyanobacteria. Fast-growing plants such as Ambulia, Cabomba, Hygrophila polysperma, Indian fern, Stargrass and Rotala rotundifolia are all useful for uptake of nutrients. If Submerged plants are not suitable, Emersed+ plants may be preferred.

  7. A 3-4 day blackout can be immensely useful for “knocking back” the Cyanobacteria. A blackout includes keeping the tank light off for several days and, if possible, covering up the sides of the tank to prevent ambient light from entering. While this isn’t a permanent fix, a blackout can be implemented to kill off a large portion of the bacteria while other variables such as lighting are then changed. It is preferable to do a water change after this blackout to clean up any dead bacteria and to help remove any excess nutrients that the dead bacteria has created.


Antibiotics: To use or not to use?

Whilst this is a personal decision, and some do recommend the use of Antibiotics (ABs) against Cyano, we personally recommend against it for several different reasons. Antibiotics have to be used with a lot of caution as they have consequences for your fish - the effect of ABs lessens when used more than once, and the risk of Antibiotic resistance in the tank increases - along with consequences to the environment as the tank’s waste water goes into our sewage system and affects Antibiotic resistance in humans. Along with this, several Antibiotics including erythromycin, can kill the beneficial bacteria in your filter which may cause Ammonia, Nitrite and Nitrate spikes, leading to stress and disease in your fish if not dealt with correctly.

As Cyanobacteria often bounces back if the cause is not corrected, we believe a tank blackout is just as effective as Antibiotic treatment and has less consequences for fish, us humans and our environment.



Cyanobacteria were one of the first photosynthetic forms of life on Earth and are found in almost every aquatic environment on the planet. This makes the bacteria quite diverse, so it’s known to be difficult to overcome. Like Algae, a small amount of Cyano is a normal part of your tank’s ecosystem - however, too much can cause problems for the health of your tank. Cyanobacteria requires patience and effort, but once the balance is found, it is well worth it. If you have any questions about eliminating Cyanobacteria, feel free to contact us, or have a look at a local forum such as the FNZAS for opinions and advice from other hobbyist fishkeepers.

Algae Cells

Green Algae is an umbrella term for the many types of algae which are common in all types of freshwater aquariums. Green algaes often boom and then decline and are a normal part of every tank, however while present, green algaes can be troublesome for the planted tank and can easily cover the glass or cloud the water.

Quite often green algae is indicative of two major components being out of balance: Lights and nutrients. For example, some types such as “green water”, can imply an imbalance such as too much sunlight or, more importantly, excessive nutrients. Others, such as “green spot algae” or “hair algae” are hard to avoid even in healthy aquaria, but are especially common in new aquariums.



Green Water:

Green water is made up of algae particles are suspended in the water (they don’t require anything to attach to like most types of algae) and is often found in high-bioload aquariums like Goldfish aquariums, or tanks exposed to a lot of sunlight. The fix for Green water is usually a simple one, and involves changing some basic conditions in the fish tank:

- Water changes! We’re going to sound like a broken record with this recommendation, but removing excess nutrients is really important for fixing many sorts of algaes. If water changes have no effect, it could imply one (or several) of three things: 1. Your water source contains high Phosphates or Nitrates, 2. The organisms in your tank are making a large amount of waste very quickly or 3. Your lighting is significantly out of balance. There are often multiple components adding to algae growth, however even if water changes appear to make no difference, they should help reduce your nutrient levels and your fish will always appreciate the clean water!

- If your tank is near a window, try blacking out the back and sides of the tank with black card, plastic or paint. If this is not possible, removing the lights on top of your tank or only using them for viewing may be of help. Cutting back your light hours to be between 5-10 hours a day can be helpful in preventing several kinds of algae.

- If your tank is outside and reducing the excess light isn’t possible, a UV sterilizer can work wonders for preventing Green water.

- While fixing the problem, a 3-4 day blackout can be very effective for significantly reducing the amount of Green water present. A blackout will help to prevent too much algae from “bouncing back” when you make the changes above. However, it’s always worth remembering that a large die-off of algae can create a Nitrate spike and a water change is recommended afterwards. In tanks with inadequate filtration, an Ammonia or Nitrite spike is also possible.



Green Spot Algae:

Green Spot (GSA) commonly grows on plants, ornaments and glass and is typically very difficult to remove without the aid of a razor (an old credit card is also often used instead). These algae types often “boom” in new tanks, but are also often caused by intense lighting or long lighting hours. Many also feel that it is caused by an imbalance of nutrients, including too low CO2 and too low Phosphates. While these algaes are normal and a small amount is nothing to be worried about, the following methods can be used to help control it:

- Water changes or or methods or reducing the build-up of nutrients such as Nitrates.

- It may be recommended to increase phosphates to maintain a level around 2-3ppm.

- Increasing CO2 using either a liquid carbon supplement, DIY CO2 or pressurized CO2 can be used, as this will also help aid in the growth of your plants. Growing plants are often very desirable for decreasing algae levels.

- Reducing lighting hours can be very beneficial, and many tanks only need lighting to be on for anywhere between 5-10 hours. Some also feel that raising artificial lighting upwards can help, as keeping the light close to the tank can cause intense lighting on the glass. Using good output angles, such as with the aid of reflectors on Fluorescents, can also help intensify the lighting in the correct direction and away from the glass.

- Fast growing plants are less likely to develop this algae on their leaves, and thus they can be used to help with the uptake of nutrients without being out-competed by the algae.

- Bristlenoses can be used to help eat this algae, but it is always important to remember that the addition of fish adds to the bioload of your tank (and thus the overall nutrient levels). Every fish also has specific needs and should not be added to a tank that they are not suited to live in.


Michelle Wimp 1

Above: Green Dust Algae and Brown Diatoms growing on a rock. Photo Credit: Michelle Whimp

Green Dust Algae:

Green Dust Algae develops a “dusty” film over ornaments, plants and glass, and is also very common in a new tank. Poor lighting quality, long light hours and too intense lighting may be to blame, however when present in a new tank, it is often recommended to simply leave the algae as it tends to go away after a couple of months as the tank matures.



DSC 5027

Above: Green Hair Algae

Green Hair Algae:

“Hair Algae” can refer to many types of algae, but here we are referring to the “fuzzy” algae that grows short and attaches itself to ornaments - quite often driftwood. Like Green Spot algae, Hair algae can be due to intense lighting or long lighting periods and reducing light intensity is often recommended. High nutrient levels are also believed to be a cause, along with low CO2. Hair algae is typically present in low amounts, however it can quickly take over ornaments. Some, though, even like to use this algae to enhance “aquascapes”!

- Reduction of light intensity, such as by raising lights or changing lighting type or quantity (eg. going from a “high light” T5HO to a “low light” T8) may help.

- Like GSA, lighting hours can play a big part. Reducing the time your lights are on even by an hour may provide results. 5-7 hours is typically recommended for a high-light tank, 7-10 hours is typically recommended for low-light tanks.

- Water changes, again! Water changes will help reduce your nutrient levels, and thus gives the algae less nutrients to feed on.

- Increasing CO2 whether by using a liquid supplement, DIY system or pressurized system, can help increase the nutrient uptake by plants and thus may help plants out-compete this algae.

- Siamese Algae Eaters are known to eat this algae, however these fish get large and need groups of 5+. Adding these fish will also add to the bioload of the tank, which may increase the levels of different kinds of algae not eaten by the SAEs.



Green String Algae:

Green String Algae can refer to several kinds of algae which grow long filamentous strands which are not attached to any surfaces. It can vary in texture, from a wool-like texture to slimy mats. String algae can become very problematic as it blocks out light to plants and picks up debris, however it can also be beneficial as a host to microbial colonies and as a food source for some fish. Despite there being several different kinds of algae under this description, the treatment to reduce these algaes is often similar.

- Like other algaes, intense lighting or long lighting hours can impact the growth of this algae.
- Increasing flow will help to prevent this algae from forming mats in the tank, and thus prevents it from blocking out light to other plants.
- Excess nutrients can play a big role for this algae to thrive. The “slimy” type of Green String algae, specifically, thrives on excess Iron. It may be worth reducing any fertilizers dosed, or switching to substrate fertilizers such as “root tabs”.
- Many recommend manually removing this algae with a tool such as a toothbrush, which will easily pick up the strands of algae.
- Some fish, such as American Flag Fish, thrive on this algae as a part of their diet. However, like all other fish, these fish have specific requirements including requiring groups of 5+ and preferring harder waters.


Blue-Green Algae:

Blue-Green Algae is in fact not even an algae at all, and is a type of bacteria called Cyanobacteria, which you can read all about here.


Still got Algae problems? Feel free to contact us or perhaps use the forum hosted by the FNZAS (Federation of New Zealand Aquatic Societies) for opinions from other local hobbyists.