Setting-Up a Freshwater Aquarium

Common Mistakes New Owners Make*

Starting Too Small

The smaller the tank, the more difficult to maintain because when the water volume is small, key water parameters change very quickly, leaving no room for error.

Adding Fish Too Soon

Aquarium water should be treated to neutralize harmful materials, and allowed to stand for a day or so to allow dissolved gases to escape and the pH to stabilize. Only then is it safe to introduce fish to the aquarium.

Adding Too Many Fish at Once

The new aquarium can only support a full load of fish after the bacterial colonies have fully established. Start with only a couple of hardy fish.

Keeping Incompatible Fish

Although it is appealing to choose your fish based on its appearance, you should always research each species before choosing tank mates. Try selecting peaceful fish that thrive in similar water conditions.


During start-up feed the fish no more than once per day. During critical times when ammonia or nitrite levels are high, withhold feeding for a day or two to reduce the wastes being produced.

Insufficient Filtration

Keep an eye on the filter to make sure it's working appropriately for the size of your tank. If it's not, you might have to get a bigger filter.

Not Testing the Water

Before adding the fish the pH, hardness, ammonia, and nitrite levels of the tank should be tested for a baseline record.

Not Changing the Water

Don't forget to keep your aquarium clean of wastes by vacuuming the gravel and removing some of water and replacing it with fresh water.

*List based on Shirlie Sharpe's article on mistakes commonly made by new aquarium owners.