After setting up your aquarium it can very tempting to immediately head to the pet store and buy a bunch of fish. Unfortunately, if you do this, you’ll often find your new aquarium inhabitants upside down within a week. This is something that happens to many new aquarists.
It can be very demotivating to have all your fish die almost instantly, but fortunately these unnecessary fish deaths can easily be prevented by cycling your aquarium.
All new aquariums go through a stage where they are a toxic, extremely dangerous environment for any live animal before turning into a healthy system. During the ‘toxic’ stage, beneficial bacteria colonies that can turn wastes into less harmful substances establish in the filter and gravel, but unfortunately, they take a while to do so. This is called the nitrogen cycle.
To understand when your aquarium is ready to add fish and what you should do if you’ve already introduced them, it’s important to know what the nitrogen cycle is first. Keep reading for more info on the nitrogen cycle or skip to how to cycle an aquarium.
The nitrogen cycle
The nitrogen cycle and the growth of beneficial bacteria are triggered by the presence of ammonia (NH3), which is released into the aquarium water as soon as fish feces, uneaten fish foods and rotten plants start breaking down.
Ammonia is very toxic to all aquarium inhabitants, and thus, ammonia levels should be kept at 0 ppm (parts per million) at all times if there are fish in the tank. This is where the cycling process comes in.
- If you introduce fish in an uncycled aquarium and test the water regularly, you will notice the ammonia levels rising around the third or fourth day. Nitrifying bacteria species, often called ‘beneficial bacteria’ by aquarists, will now start to do their job.
- As the bacteria settle in the filter and gravel of your tank and start eating the ammonia, you will notice nitrite (NO2) levels rising. Nitrite, which is a by-product of the ammonia-eating bacteria, is also very toxic to fish and can kill/permanently damage them even at very low levels. Luckily, a second colony of bacteria should now start forming.
- Nitrites will be converted to much less toxic nitrates by this second colony. Nitrates are the final product of the cycle, and will stay present in the aquarium unless a water change is done. Plants also use nitrates as nutrients, but they are no replacement for regular tank maintenance.
- As soon as nitrates are present in the aquarium and ammonia and nitrite levels have dropped to 0 ppm, the aquarium is ‘cycled’. This means that after a water change is done to reduce the nitrate levels to <30, fish can safely be introduced. You may now run out to the store (just don’t introduce too many fish at once).
How to cycle an aquarium
There are several ways to cycle an aquarium; most involve introducing ammonia in the tank to trigger the growth of beneficial bacteria colonies. I recommend getting a water testing kit before starting the cycle – this way you can monitor the water values and determine in which stage of the cycle the aquarium is.
A liquid tester like the API Freshwater Master Test Kit is much more accurate than test strips and cheaper in the long run as it can last you many years.
Cycling with fish: not a good idea
The oldest and most common way to cycle an aquarium is cycling with fish. This means some cheap fish are put in the tank so the ammonia they excrete starts the cycle.
It is often recommended by pet stores because it means extra profit for them when fish die, but cycling an aquarium this way actually takes a long time, requires a lot of water changes to keep the fish alive and usually permanently damages or kills the fish used. Luckily, there are plenty of cruelty-free and easier ways to cycle an aquarium.
Cycling with food
As mentioned earlier, uneaten fish food is broken down into ammonia, which is exactly what we want in this case. A large, uncooked prawn or fish food is added to the tank and left there to decay until the tank is cycled, and that’s it.
This method is not entirely risk free, because rotting food often attracts unwanted bacteria and turns the tank water very dirty. A big (90-100%) water change should always be done before introducing fish to a tank cycled this way.
Cycling with ammonia
Pure household ammonia is sold in garden stores and some supermarkets as a cleaning product. Ammonia is also sold in smaller containers specifically for aquarium use by several brands, such as this one. Add about a drop of ammonia per gallon of tank water. After ammonia levels drop to zero, repeat this and wait until ammonia and nitrites are both at zero.
Your aquarium is now ready for fish. A large water change should be done to lower the nitrates to <30 ppm before introducing them, and if you’re not ready to introduce them yet, be sure to keep adding ammonia to prevent your beneficial bacteria from starving.
Seeding the filter
Using cycled filter media that already has the right beneficial bacteria colonies in it can quick-start the cycle in your aquarium. This way you can add fish instantly, but you do run the risk of introducing any diseases or pests from the ‘donor’ tank into the new one.
If you don’t own a cycled aquarium, you can ask friends who own an established tank or pet/aquarium stores – they might be able to supply you with some seeding material. Use the media as quickly as possible – it should be transported in some water from the tank it was in and it should never sit for more than ~1 hour before it is put in the new tank’s main filter or a separate one.
If you need to let the used media sit for a longer time, put an air stone into the bucket to provide the beneficial bacteria with oxygen and flowing water and prevent them from dying.
Filter bacteria can be bought from pet-/aquarium stores in a bottle. It is recommended to always check the expiration date on these products as they can usually only be stored for about a year, and to keep them in a cool, dark place like the fridge (not the freezer!).
Don’t assume you can add fish right away: these products are best used as a ‘kickstart’ for your cycle so the process doesn’t take as long. They do work, though, especially when combined with a high quality water conditioner like Seachem Prime to remove traces of ammonia and nitrite.
Cycling your aquarium before adding any fish is one of the most important steps to achieve a healthy little ecosystem, and it’s one you should never skip.
The ammonia and nitrite spikes that result from failing to properly cycle an aquarium cause fish death and weeks/months of trouble, constant water changes, having to buy expensive products, and can completely ruin the hobby for you.
If you have any more questions about cyling an aquarium or if you have something to add to this article, be sure to leave a comment below. Happy fishkeeping!