How to Avoid Killing Your Fish in Your New Aquarium 

Even the best aquarium you can buy has been set up to keep your fish alive for only seven days.  This is due to the  lack of bacteria present in the filter bed of the aquarium.  The bacteria are necessary to break down and convert fish excrement and urine into harmless by-products which the plants in your aquarium use as fertilizer for growth.

To prevent premature fish death your aquarium should have a fairly large quantity of these bacterial colonies.

Sources of Beneficial New Aquarium Bacteria

Bacterial usually builds up over a period of time, and is highly concentrated on the under gravel filter. When buy an aquarium with an under gravel filter, ask for a filter that has been used or see if you can get part of the gravel bed from an old operative filter.

If these options are not available, add a tablespoonful of flower pot soil or borrow a little mulm from a fellow aquarium owner.  "Mulm" is a brownish, fluffy material that accumulates in the aquarium.

"How to Avoid Killing Fish in Your New Aquarium" contributed by Brantley Garrett