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Keeping the Water Clear

Is the tank overcrowded?

By Al Castro

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Q. I have had a 10-gallon aquarium for nine months. It contains 10 pounds of gravel, one airstone and some plastic plants. The only source of filtration is a small outside overflow power filter. The inhabitants of the aquarium are two pearl gouramis, one dwarf gourami, one opaline gourami, three white cloud mountain minnows and two Corydoras julii catfish on the bottom. I thoroughly vacuum the gravel and change 40 to 50 percent of the water every two weeks. I change the filter cartridge every four weeks. The aquarium looks good for about four days after I clean it, but I get cloudy water during the remainder of the two weeks between maintenance. This doesn't seem to bother the fish though. They are extremely healthy and active. Once a day I feed all the fish can eat in two or three minutes. Ammonia levels are always at zero, and the pH is 7.0. Is the aquarium overcrowded?

I know the limit of a 10-gallon aquarium is 20 inches of fish, and I have about 14 inches, not including the catfish, which total about 4 inches. (I learned you don't count the bottom-dwelling catfish in the limited number of inches.)

The fluorescent light is on only four hours a day to prevent excessive algae and green water, which happens when the light is left on eight hours daily. Any advice on how to correct the problem with cloudiness would be much appreciated.

A. Although I can't actually see your aquarium to be sure that my ideas are correct, I do have a few things that might help you. However, the first thing I want to do is discuss the myth about catfish that you refer to. Why wouldn't you count your bottom-dwelling catfish? They are in the aquarium taking up swimming space, eating food, polluting the water and so on, just like the rest of the fish. Catfish are real fish, with real needs, that must be considered when you set up your aquarium. They count as much as any other fish in the aquarium.

The concept of 2 inches of fish to a gallon of water is only a guideline based on the oxygen needs of schooling community aquarium fish. It is not a hard and fast rule because different fish have different requirements.

Your aquarium is not overcrowded from an oxygen requirement standpoint, but this is largely because of the large number of gouramis that you have. (Remember that gouramis have an accessory breathing organ that allows them to effectively remove oxygen from atmospheric air, and that your catfish have a similar but less effective method of doing the same thing.) However, your aquarium is going to seem rather cramped when the gouramis reach full growth. Don't rely on guidelines to provide all the answers (an 18-inch shovelnose catfish would not survive in your 10-gallon aquarium). Learn about the future needs of fish, not just their present needs, before you purchase them.

My first thoughts about your cloudy water are hampered by not knowing the color of the cloudiness. I am assuming it is a grayish or whitish color and that it is produced by bacteria. Yes, you are cleaning the aquarium regularly and you are changing the water regularly, but I wonder if you are not over-cleaning.

Your description sounds like a classic case of "new tank syndrome," without the problem of elevated ammonia levels. Some bacteria are necessary for a healthy and clean aquarium. Your efforts are so good that you may be preventing the normal establishment of enough beneficial organisms that help clean things up. My best recommendation is to gravel-vacuum only half of your aquarium at a time and to change only 20 to 25 percent of the water, which should have similar temperature and water quality to the existing aquarium water. This will prevent the shock of sudden changes from affecting both the fish and the established micro-organisms in your aquarium.

This is just a reminder, but you should be aware that green water can still develop with only four hours of fluorescent lighting if there is sufficient daylight in the room to help it grow. Check to make sure that the cloudiness does not have the characteristic greenish tinge of suspended algae before you do anything.

Lastly, I am concerned about your only feeding the fish what they can eat in a two- to three-minute period. I know that I can't gauge food quantity well enough to do that. Are you sure that every fish is getting enough to eat? If this is the same batch of fish that you started with nine months ago, are they growing at the rate they should? After nine months, your pearl gouramis should be 4 or 5 inches long, your opaline gourami almost the same, your dwarf gourami should be almost 3 inches and your white clouds should be about 1½ inches each. If your fish do not measure close to these sizes, maybe you should consider another feeding of an equal amount each day.

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