Pet Talk: Let the fish clean up for themselves

If that slimy fish tank you have needs a good scrubbing, think twice before you get out the brushes and the Mr. Clean.

It's best not to try any household slime-stoppers - in fact, it may be best to let your fish do all the work.

What we might call slime is actually mucous secreted from the fish in order to create a pleasing environment and combat high alkaline pH levels in tap water.

Most fish work on a cleaning cycle that lasts about two to three weeks, says Dr. Donald Lewis, professor in the Department of Pathobiology at the College of Veterinary Medicine & Biomedical Sciences at Texas A&M University.

The cycle begins when fish are first introduced into a new aquarium. Most owners purchase a tank and fish at the same time, placing fish into the water as soon as the tank is filled.

This instant plunge causes the fish to secrete mucous as a way of protecting itself from the high level of ammonia found in tap water resulting from the breakdown of organic matter, Lewis said.

The mucous secretion is a population of bacteria, and the first step a fish takes to deal with the excess ammonia. The bacteria that are produced from the mucous convert the ammonia to nitrites, which in turn covert the nitrites to nitrates.

By the end of the cycle, all three compounds exist and balance out the system.

Plants can also be used to help stabilize the environment by absorbing the ammonia, nitrites, and nitrates from the water.

The cycle begins again when the current system is disturbed by: fish excrements, excess food resting on the aquarium floor, adverse environmental conditions, or parasites, Lewis said.

Instead of spending so much time cleaning out your fish tank, or buying new fish, Lewis suggests some preliminary techniques:

Install an underwater gravel filter. It is driven by the air filtration system and functions as a water cycle to prevent the water from layering when debris and mucous arise.

Place gravel, rocks, and other accessories into the aquarium or tank.

Pour the water into the tank.

Wait at least two to three weeks before introducing the fish to tap water. Unless the fish you purchase is very resilient.

Consider placing plants, oysters, or seashells in the aquarium. Plants are very beneficial in absorbing the excess ammonia and nitrates present and oysters and seashells can act as a buffer keeping the water only slightly alkaline.

One thing to remember is that the amount of slime produced is always dependent on the type of fish and environmental conditions.

For instance, most tropical fish originating in South America prefer slightly acidic water and are very sensitive to high ammonia levels, while others like cichlids prefer slightly basic water and can tolerate ammonia.

All fish have their own unique pH preference and even the most properly maintained aquariums have a little mucous sitting on the surface, Lewis adds.

The next time you see the characteristic mucous and feel the slick surface of your tank, it might be your fish just doing a little tidying up.

Pet Talk is a service of the College of Veterinary Medicine, Texas A&M University.