The Easy Guide to the Nitrogen Cycle for Aquariums

Are you getting started with your first fish tank? Perhaps you have heard of the “aquarium cycle,” which involves complex graphs and scientific terms that can be overwhelming. No need to panic! We will explain the nitrogen cycle in this short guide.

What is the Nitrogen Cycle for Aquariums.

The nitrogen cycle basically describes how nature creates food (in the form of microorganisms and plants), fish eat the food and produce waste, and then nature breaks down the fish waste so that it can get converted into food again.

An illustration of the nitrogen cycle for aquariums.

When aquarium hobbyists talk about the nitrogen cycle, they are usually referring to the specific part of the cycle where the fish waste turns into toxic nitrogen compounds like ammonia, nitrites, and nitrates. These nitrogen compounds can potentially kill our fish unless we make sure we have plenty of microorganisms (also known as beneficial bacteria) and plants to consume the waste products.

For the purposes of our illustration, let’s use yellow, brown, and blue M&M’s to represent the three toxic nitrogen compounds:

– Yellow = ammonia (which is very toxic and can burn fish gills and skin) – Brown = nitrite (which is somewhat toxic) – Blue = nitrate (which is not as toxic as ammonia and nitrite)

Step 1: Whenever your fish goes to the bathroom, some ammonia is produced.

Step 2: Beneficial bacteria #1 eats the ammonia and produces nitrites.

3rd Step: Beneficial Bacteria #2 then eats nitrites, and produces nitrates.

Step 4: The fish continue to eat food and produce waste, which gets processed from ammonia and nitrites into more nitrates.

Step 5: Eventually, the amount of nitrates will build up and can become harmful to the fish in high amounts. You must remove the nitrates either by doing a water change or by using aquarium plants. (The aquarium plants consume the nitrates to produce new leaves.)

Cycling an aquarium is simply the act of making sure that your tank has enough biological filtration, such as beneficial bacteria and aquarium plants, to ensure that any ammonia or nitrites are eliminated quickly. If you have ammonia test strips and multi-test strips, ideally you should measure 0 ppm ammonia, 0 ppm nitrites, and usually some amount of nitrates in your tank water. You need to get rid of any dirty water from your tank and replace it by clean water if the nitrates exceed 40 ppm.

How long does it take for an aquarium’s cycle to complete?

It can vary depending on the situation, but it usually takes between a few weeks and months. You can speed up this process by buying a bottle of live nitrifying bacteria, getting some used filter media from a friend, or growing live plants (which also come with beneficial bacteria on them). Read the entire article to learn how to cycle an aquarium.

Most hobbyists will answer yes or no to the question of whether their aquarium is cycled. In reality, the answer is a little more complex. Instead, we should be asking, “How much beneficial bacteria does the tank have, and is it enough to treat the waste produced by the fish?” For example, if you have a “cycled” aquarium with 3 neon tetras and then suddenly you add 200 neon tetras, that aquarium no longer has enough beneficial bacteria to immediately convert all that waste into safe nitrates.

How do I increase my biological filtration?

So, how can we ensure that the aquarium has enough biological filtering to deal with toxic nitrogen compounds? One easy way is to of course add more aquarium plants, which will happily consume the ammonia and nitrates produced by your fish’s waste. Just remember that if you don’t have enough fish waste to feed your plants, they could starve to death, so you’ll need to supplement with a good, all-in-one fertilizer like Easy Green.

It is common to believe that purchasing more filters will increase the number of beneficial bacteria in your aquarium. Beneficial bacteria can grow on all surfaces in an aquarium. This includes glass walls, gravel, decorations, and even glass walls. Buying more filtration simply means you have greater capacity to hold more beneficial bacteria, but if you only have a few fish, your decor alone may have enough surface area to colonize the necessary beneficial bacteria.