One of the crucial factors when setting up a new fish tank is to determine how many starter fish can be safely added; once the initial waiting period has been finished. You must be careful not to add fish to the point where the population is too large. If this occurs, the new fish will actually poison themselves with the toxins they create.
It takes about six weeks before the beneficial bacteria that were not there in the beginning to created a strong enough population. Once established, they eliminate all the ammonia exhaled and created by the fish as they live. A proper biological filter eliminates this as fast as it is manufactured. In a new fish tank, this overproduction of ammonia cannot be removed by the actual population of denitrifying bacteria strains. Over time, this overproduction of ammonia gradually builds up and causes severe problems. The starter fish literally will poison themselves from the production of their own wastes.
There are lots of rules of thumb that have been offered to help a novice aquarist select the proper amount of starter fish that can be safely added to the new aquarium. We can't tell you about all of them, but will state the one we use to determine the bioload the tank should start with. Actually our guidelines need to be broken into two separate parts, The first is for the brand new aquarium set-up that is just started. The second will be elaborated in a following tip as it refers to the ultimate load an aquarium can safely support once the biological filter and its beneficial bacteria have been established.
For a new aquarium, we recommend - at the very most - one inch of starter fish per gallon capacity of the fish tank.
For example: if the newly established aquarium is a ten gallon tank, we recommend never exceeding ten inches of fish. In this initial calculation, we include the entire length of the fish; from the head to the end of the tail.
As mentioned, if the tank is overloaded with life when a bacterial filter bed is non-existent,discus fish, or still in the process of maturing, the fish will excrete more ammonia than the initial bacterial colonies can ever hope to reduce. In this case, the concentration of ammonia and/or nitrite rapidly rises in the water. To be brutally honest, in the very beginning, the less fish in the tank; as long as there are some to provide a biological load and create some ammonia naturally, the better.
It is much wiser to have a much lighter biological load and allow the bacteria to multiply in lower ammonia levels. You should try to avoid forcing the fish to live in highly toxic conditions that ammonia creates. As long as there is a concentration of ammonia in the water, the bacterial population will continue to increase until all that is produced is eliminated instantaneously.
Actually, in many cases, the ammonia is not as toxic if the pH of the water is low. This phenomenon will be discussed in a later tip. But, in any case, once the bacteria have been given enough time to establish and allowed to populate enough to reduce ammonia almost instantly, it is the consequent build-up of nitrite that is the most lethal.