If I had a second title, it would be “How not to kill your fish.” Please keep reading.
You may not find out at the pet store, but setting the nitrogen cycle in your new aquarium is the most important step in maintaining a successful fish. Why? Because most living things produce toxic ammonia when they eat, grow, breathe, and drink. We can shower or remove toxic ammonia, but an aquarium fish has to live in a closed environment. What goes in stays behind and poisons the fish if not removed or rendered harmless. That’s where the nitrogen cycle comes in.
We call it the nitrogen cycle, because toxins like ammonia and nitrite are nitrogen compounds, and those are all the chemical words we need for now. Another important word is little critters, which some people call bacteria. There are little critters everywhere and some of them are very good for your aquarium. In fact, different types of insects eat the toxic ammonia and nitrites that fish, uneaten food, dead plants and the odd curious cat introduce into the aquarium.
When your aquarium has enough good insects, they will turn all the toxins into plant food. Almost like magic, the good critters enter your aquarium. All you need to do is feed them and give them a few weeks to grow BEFORE adding the fish. Good little microscopic insects will eat flake foods or even small pieces of raw shrimp or fish. They live primarily on gravel and filter elements, so if you have an old filter or gravel from an established aquarium, try using a few in your new aquarium. You may be able to speed things up by adding one of the products that contain inactivated bacteria. However, the process will still take some time.
The main task of the aquarist while all those good critters are growing is to wait a few weeks. The wait gives you the opportunity to get a test kit to measure at least ammonia and nitrite, and do some research on the species of fish you want to keep. Everyone needs different things. You can also add plants and operate the light and filter, but NO FISH YET.
After all that difficult waiting, you can test your water for ammonia and nitrite. When both measurements remain at zero for a couple of days, the nitrogen cycle is working and the aquarium is ready for fish. Bacterial colonies will grow large enough to handle toxins, but they can only handle a limited amount, so don’t overwhelm them with too many fish or too much food. If everything works as it should, you will have a well balanced aquarium. To maintain that balance, change about 20 percent of the water each week, and don’t forget to use a good water conditioner.