A Red and a Tiger Oscar in an aquarium.

Establishing an Aquarium

A successful, long-term aquarium begins with a good foundation. Although these initial “groundwork” steps will determine the health of your aquarium for the rest of its life, this part of the process is often overlooked or carried out incorrectly in haste. A properly cycled aquarium is a result of patience.

So what do we mean by “cycled”? First, we must understand that there are 3 major types of filtration. In brief, the motorized filter on your aquarium will catch debris and provide “mechanical filtration”, and the carbon in these filters will provide “chemical filtration”. However, there is a third filtration type that must be grown rather than simply installed: “biological filtration”. Establishing this 3rd type of filtration is what it means to have a cycled aquarium.

The process of establishing a biological filtration is fairly simple. After filling your tank with water, you will first want to use a dechlorinator (easily found at any fish shop) to remove the hostile chlorine found in all tap water. After this, you will likely want to add freshwater aquarium salt. This salt will raise the immune system of the fish and prevents fungus and many parasites. Now we can begin “growing” our biological filtration.

The Nitrogen Cycle

There are two species of bacteria that we must grow in order to establish our biological filtration. The first, Nitrosomonas sp., takes the ammonia produced by the fish and converts it into less harmful nitrites. The second, Nitrospira sp., takes these nitrites and converts these into still less harmful nitrates. The only practical way to remove nitrates is through water changes. This process of bacteria converting these chemicals ultimately into less harmful nitrates is what is known as “the Nitrogen cycle”.
Several Silver Angelfish in a planted tank.

Establishing The Nitrogen Cycle

Take a look at The Nitrogen Cycle. We need to replicate this process in our aquariums else the harmful ammonias produced by fish waste and uneaten food will remain. This begins with the introduction of ammonia (either through the addition of the first aquarium fish or the addition of a water conditioner with ammonia). This ammonia will provide the “food” for the beneficial bacteria we are trying to grow in the filter. While these bacteria are naturally occurring, there are products (like Seachem’s Stability) which are concentrated bacteria colonies which can reduce (but not eliminate) the wait time involved.

The first colonies of these bacteria are usually established within a few weeks of adding the first ammonia, and green algae in the aquarium is evidence of the bacteria’s presence. During this process, you may want to test the water chemistry every few days and make sure the ammonia level is going down.

At this point we can add more fish -- a few at a time. These fish will cause the ammonia to rise, and the bacteria colony will grow over the next few days to match the new “food” levels. Again, you can do water chemistry tests and make sure your ammonia levels are gradually depleting instead of rising. If it gets a little high (above 20 ppm), you should do a partial water change to bring it back down. Now you’ll add more fish, the ammonia will rise (careful it doesn’t get too high), the bacteria colonies will grow and it will drop back down. Each time you add fish, this process repeats.

This is the basics of cycling an aquarium. You will want to test your water frequently to keep an eye on the chemistry and make sure nothing is getting out of hand. If the ammonia or nitrites are a little high, you may be overfeeding, you may need some additional biological filtration media (places for these bacteria to live), or your aquarium may be overstocked. Whatever the reason, do a quick water change, test the water afterward, and see if it goes up or down over the next several days.