By David A. Lass
Let's start with understanding one basic thing about algae in your aquarium – algae itself is not bad. Too much algae, or the wrong kinds of algae are what is bad. Every healthy aquarium that has the normal complement of fish has plenty of algae – good algae. Those who have seen the absolutely pristine planted aquariums of the Amano school of planted aquariums, know that these systems are very high tech, with lots of lighting and carbon dioxide injection. Also, with the exception of a few different types of tetra fish, all of the livestock in an Amano aquarium are in there because they eat algae. But, most people don’t have these aquariums, so let’s talk about a normal aquarium where the stars of the show are the fish; and the live aquatic plants are there because they look good, make the fish feel more comfortable, and also help achieve a natural balance in the aquarium.
"Nuisance" algae can take a number of forms. Green water is a common algae problem. Green water is algae living in suspension in the water column. Slime algae is a phylum of its own – cyanobacteria – and is in-between a plant and a bacterium. Hair or brush algae is little tufts all over things in the aquarium. All of these, and other nuisance algae, is caused by two factors.
Too Much Light
Too Much Food
Aquarium light is easy to control by putting the aquarium lights on a simple timer, and allowing the lights to be on for between 8 and 10 hours each day. Food for algae is in the form of nitrogen and phosphate, and both of these come as a result of feeding your fish too much and/or too often. Fish food in either form (having gone through the fish or sitting around the aquarium uneaten) is food for algae, and too much of it makes for nuisance algae.
The best way to limit problem algae in your aquarium is to have plenty of fast-growing live aquatic plants. Live aquatic plants compete with algae for food, and since true aquatic plants are a "higher" order than algae, they can usually successfully compete with algae for food. Having lots of growing live plants essentially starves the algae, and will keep the algae limited to a beneficial and minimal amount.
There are a number of fishes that are sold by your local fish stores as "algae-eaters." Some of these, although they may eat algae, are not very good for an aquarium. The two most common "algae-eaters" that are sold are common plecostomus (also called sucker mouth catfish or plecos) and Chinese algae eaters (CAE's). Both of these are inexpensive, and when they are small they will, indeed, munch on algae – but not on the nuisance algae, only on the good algae. Plecos and CAE's will do absolutely nothing for green water, brush algae or slime algae/cyanobacteria. Not only will they really not do much for controlling algae, but these two fish get large – common plecostomus can grow to 18 inches, and Chinese algae eater's to 8 inches – and they can start sucking the slime off the sides of fish, especially larger disc-shaped fish such as angelfish or discus.
There are a number of aquarium fish that are better for controlling algae in an aquarium. They are a little more expensive than plecos or CAE's, but they are well worth the price. Otocinclus are dwarf sucker mouth catfish, and Ancistrus look like a pleco, but they only grow to 4 or 5 inches. Siamese Algae Eaters (SAE's) are excellent at eating all kinds of algae. Some of the fancy "L-number" plecos are good algae eaters, but an equal number of them are, in fact, not algae eaters at all, but require a "meaty" diet. And one final thing to mention, all of the fish that are good algae eaters need to be fed vegetable based foods. In almost all aquariums, the good algae eating fish will rather quickly eliminate most of the algae, and will soon be looking around for more to eat. They need to be fed either fresh vegetables such as potato or zucchini, or flake or wafer dry foods that are high in vegetable matter.
Snails and shrimps are often sold as a solution to algae problems. Neither of them will do anything for green water or cyanobacteria, but many of the shrimps will do a very good job of eating algae on aquatic plants. There are a number of shrimps on the market now that are sold as "Amano" shrimps, and while there really is only one true Amano shrimp, most of that shrimp's close relatives will also do an excellent job of eating algae. The only problem is that you need a lot of them, somewhere on the order of 1 or 2 per gallon. Most snails are really a toss-up between whether they may eat algae versus the fact that many of them will eat aquatic plants. The only snails that I really recommend for a planted aquarium are the Malaysian live-bearing snails, also called "trumpet" snails.
Control algae in an aquarium by using the proper amount of light, feeding the proper amount of food and having lots of live aquatic plants. And be very careful in what livestock you buy for assisting you in dealing with problem algae.