One of the biggest problems all fish keepers need to deal with at some point is algae.
If you just set up a tank with fishes and leave it alone, it’s almost guaranteed that within 2 weeks, it will look like this –
All the glass surfaces will be covered by algae. All the gravel and decorations are covered by algae, and the water may be green due to microscopic algae.
Not exactly pretty eh? Truth is, fish keeping is not as easy as it appears to be. Fishes can be as high maintenance as other pets, approaching the level of a significant other.
It can be due to a million different things, such as nutrient imbalance, inappropriate lighting (intensity, duration, and spectrum), and decomposing waste.
This post is about how you can carefully set up the fish tank to manage its own algae problem, biologically. There are chemical solutions, but I don’t like having to regularly dump harmful chemicals into my tank. You can also clean the tank manually twice a month, but that’s annoying, and some types of algae are very hard to get rid of.
The biological approach consists of plants, algae-eating fish, and snails.
Plants are very important. I don’t think it matters what kind of plants, but having plants in the tank introduces competition for the nutrients both plants and algae need. It should be noted though, that plants will only use nutrients when they are photosynthesizing. For effective photosynthesis, there should be good amount of light, and more importantly, in the right spectrum. 6500K CFL works well for me. Most light bulbs sold at hardware stores will be too yellow, and will only promote algae growth, since algae are a lot less picky about colour temperature. Second thing is carbon. Everyone has a different theory about how carbon should be added, if at all. For me, Seachem Flourish Excel works well. It’s actually not carbon, but a complex photosynthesis intermediate that reportedly cannot be utilized by algae.
Nitrate is probably the most important nutrient to keep in check. It’s generated by decomposing fish waste (ammonia -> nitrite -> nitrate). While it doesn’t do anything to fishes (except at very high concentration), it’s an important nutrient for plants. Without plants to consume them, nitrate concentration will just keep going up, and an algae boom will result. Therefore, it’s crucial to change water regularly to remove nitrate if the tank is not planted. I find that in my planted tank, nitrate level never goes up.
2. Algae-Eating Fish
Some fishes will eat algae, which is great, but care must be taken to ensure that they are compatible with the water conditions (hardness, pH, and temperature), as well as other fishes in the tank. Below are some algae eaters that are compatible with most tanks, and peaceful towards other fishes.
Otocinclus catfish solves most of the problem.
They are pure herbivores, so they won’t eat most of the flake food you feed other fishes with. They are also somewhat delicate, and require high water quality (proper filtering, good pH, no ammonia, etc). They also like to rest on leaves, so I wouldn’t put them in an unplanted tank. If there’s not enough food for them, I recommend feeding them sliced zucchini. They (and most other fishes) love that stuff. My tank of about 15 fish can finish a 3mm slice in about 2 days.
They eat almost all kinds of algae. One notable exception is hair algae. They don’t touch that stuff.
You may be thinking that’s fine. There will just be a little bit of hair algae left. Unfortunately that’s not how it works. Because otos only eat other types of algae, they are applying selective evolutionary pressure to the algae population. Darwin will eventually kick in, and replace all your algae with hair algae. This is essentially how evolution works, just much accelerated. I witnessed this first hand.
So now we need a fish to eat hair algae. Siamese algae eater (SAE) is a popular choice.
They eat all kinds of algae, but especially hair/thread algae. Fairly hardy fish that eat just about everything.
Plecos are another popular choice, but they are only suitable for much bigger tanks.
Black mollies also reportedly eat hair algae, though not as much as SAE.
Just regular aquarium snails that seem to come with all plants. Some people find them unsightly, but they do clean the glass surfaces pretty well. They require no care at all.
If snail population booms, they can be removed with some lettuce.
This is my tank right now.
Almost no algae at all (only a little bit on the filter). This is about a month after I implemented this system. No maintenance required so far.
This is a 20 gallon tank with 5 random plants, 4 guppies, 5 neon tetras, 2 otocinclus catfish, and 2 Siamese algae eater. High water quality (a lot of guppy reproduction going on). 25C, pH 7.0, moderately hard. 2x15W 6500K CFL lighting. Fishes look happy, and plants are thriving (although the red plant is turning green, suggesting slow growth).
Happy fish keeping!