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Algae-Eating Fish

Good, and not so good, aquarium algae-eating fish.

Posted: October 20, 2010

By David Lass

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Algae are very often a problem for aquarium hobbyists, especially for aquarists who are just starting out in the aquarium hobby. No matter how many times fish store staff informs customers that algae (either growing on things in the tank, or the dreaded “green water” syndrome) come from too much food and too much light, hobbyists usually swear up and down that could not be the case with their aquarium.

It is often easier to suggest they buy a fish that will eat the algae in their aquarium. For green water, if the customer won’t cut down on the fish food or the aquarium light the only remedy is an ultraviolet sterilizer.

But, when it comes to algae-eating fish, the two most commonly sold fish are also the two worst: the Chinese algae eater and the plecostomus. Both of these aquarium fish are relatively cute, very cheap and very hardy.

The problem is, both of these fish also a) get much too large for the average tank and b) when they get to know that the “Flake Food Fairy” is going to drop yummy prepared food into their tank every day, they stop being at all effective in their algae-eating roles.

There are, however, a number of fishes that do make excellent algae eaters. The first group is any fish of Ancistrus genus. These are usually sold as bristle-nosed plecos, clown plecos or simply Ancistrus. These fish are excellent at eating algae, and their effectiveness does not diminish with age. Ancistrus also get to be only 4 to 5 inches in size as adults. There is a very easy way to tell whether fish are plecostomus or Ancistrus.

When in a fish net, the Ancistrus and their relatives have little bristles that come out from the side of their mouths. These are called “odontodes,” and plecostomus do not have them. Good algae eaters stick in the fish net -- bad ones don’t.

Other fish that are good algae eaters are the small Otocinclus, commonly known as dwarf sucker-mouth catfish. These aquarium fish have a bad reputation for being delicate in stores, but this is usually because they are not fed enough. Keep a piece of parboiled potato in the tank with your Otocinclus, and encourage your customers to make sure that any algae eaters in their tanks also be fed, because the fish will not be able to thrive on just the algae in the aquarium.


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robert    fairfax station, VA

11/21/2010 3:52:19 AM

My Plecostomas is 100% effective at cleaning brown algae in my 50 gallon tank. It is a workhorse and gets the job done 24/7. This is the best solution to a problem I have ever had. If it gets too big, I'll just get another one. It has not stopped eating and cleaning my algae, and it is like the Energizer Bunny- It keeps going and going and going! Very satisfied with my Plecostomas.

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