Fish Aquarium

Cycle the tank before adding fish

A new tank has no bacteria to process fish waste. Ammonia builds up and burns gills, which is what kills most first fish. Running the filter for several weeks before stocking, with a source of ammonia to feed the bacteria, lets that colony establish — a process usually called cycling.

A basic test kit for ammonia, nitrite and nitrate is the single most useful thing a new aquarist can own, because none of these are visible in clear water.

Water changes and feeding

Change a portion of the water regularly rather than emptying the tank; a full change destroys the bacterial colony you spent weeks building. Treat tap water for chlorine before it goes in.

Overfeeding is the other common beginner mistake. Feed what the fish finish in a couple of minutes and remove the rest — uneaten food breaks down into the same ammonia the filter is fighting.

Stocking

Research adult size and temperament before buying, not after. Most fish sold small do not stay small, and many popular species cannot be kept together.