How to Get Rid of "Brown Algae" (Diatoms) in Freshwater Aquaria
Brown algae can be a delicious meal or an unsightly oxygen hog, depending on the type of animal you choose to keep in your aquarium. When aquarium owners talk about "brown algae," they are actually talking about diatoms, microscopic brownish or greenish creatures with glassy skeletons. (When botanists talk about "brown algae," they are likely talking about distantly related large seaweeds.)
Understanding "Brown Algae" (Diatoms)
What do "brown algae" need to live? It's best to always remember that although diatoms can and will synthesize food using sunlight (or almost any light, for that matter), they don't need light the same way regular algae or plants need light. That is to say, the diatoms don't get energy exclusively from light itself.
Here are conditions that are beneficial to diatoms:
- Silicates (rocks or sand containing silica)
- Nitrates (a waste product of aquarium life)
- Still or stagnant water
- Hard or mineral-rich water
The two main differences between true algae and diatoms are that regular algae do not consume silicates and that regular algae can be eradicated by eliminating either the light or the nitrates. The problem most people run into with diatoms is that no matter how long you leave the lights off, the diatoms persist. And if you were able to somehow eliminate most of the nitrates from the aquarium, the diatoms would consume silicates as well, or instead.
So the first step to getting rid of brown algae is to erase the word "algae" from your thinking about this stuff.
Step two is to make sure the tank has adequate filtration (the filter system is rated for the gallon capacity of the aquarium). The aquarist should keep in mind that many of the "hang on the back" style filters can expose the water to a very large amount of light, depending on the brand of filter and the ambient lighting in the room.
Step three is to realize that even though you may have adequate filtration, you need water movement as well to discourage diatoms. You can get water movement using products called "powerheads" or "current makers." These move the water around in the tank, accomplishing two things:
- Diatoms aren't very strong and they don't swim. A current maker will prevent them from anchoring anywhere, thus preventing their growth.
- The added water movement will keep all the water in the tank filtered, instead of just a percentage.
For step four you need to do some hands-on work with the tank. Very carefully remove all plants and ornaments from the tank, leaving only substrate (rocks or sand) and hardware (filters, heaters, and so on). Wipe the diatoms off the surfaces of the hardware and try to scrub it out of the rocks or sand to the best of your abilities. You could bleach all the plants and ornaments at this time, or you could scrub them with an abrasive sponge. Either way, get the diatoms off the plants and ornaments while they are NOT inside the tank.
Step five should be pretty obvious once you remove everything from the tank. Do a 30%-50% water change (after the hardware and substrate have been scrubbed). Then return all ornaments and plants to the aquarium.
Step six is the last step, and the same as the last step on a shampoo bottle. REPEAT. Do this about every two weeks and you'll see the diatoms bloom less each time (you should only have to do it two or three times).
If these steps don't work for your aquarium, it may be that:
- your aquarium is exposed to too much light,
- there's not enough water movement in the tank,
- you keep scrubbing the diatoms off into the tank water, or
- there are too many diatoms in the substrate.