cycling your aquarium

Cycling your aquarium

The aquarium nitrogen cycle is something every fish keeper should be aware of. Cycling your fish tank is the first, and most important step in fish keeping. Which unfortunately most newcomers to the hobby miss out. A common mistake, most of us have done it. After setting up your aquarium, before you add any fish, you have to go through a process called cycling. Cycling your tank is mandatory. If this initial step is missed, your fish will die from the chemicals caused by their own waste, and uneaten food.

Aquarium Nitrogen Cycle, how to cycle a fish tank


The first harmful chemical to appear will be ammonia, which causes permanent damage and will kill your fish over time. Unfortunately this is very common among beginners.  To avoid this we cycle the aquarium by first adding liquid ammonia. After the filter media has built up ‘good bacteria’ it starts turning the ammonia into nitrite, and then eventually nitrate. Nitrate can be tolerated by the fish at low levels (weekly water changes will help remove the remaining nitrate). Once nitrate has started being produced, the cycle is complete. We call this a ”fish-less cycle”, which means a cycle without harming any fish. The fish can then be introduced.


To test these chemicals we can use a variety of test kits. Most people use a very popular and approved test kit called the API Master Test Kit. There are other ways such as test strips, but the API master test kit is both more cost effective and more accurate. The kit can last several years.  A fish-less cycle takes approximately 4-6 weeks. If you do this and are patient then you minimise the loss of fish when first introduced.

Water changes

After the aquarium nitrogen cycle is complete, harmful chemicals will still be produced, which is why we still do weekly or bi-weekly (dependant on stocking levels and filtration) water changes, amongst other reasons. When we do a water change we replace roughly 20% – 50% of the tanks water. Again this depends on the stocking levels of your tank, and your filtration. When adding new water from your tap, water conditioner needs to be added, to remove chlorine. Water changes will remove any remaining Nitrate, and will ensure clean and healthy water. Water changes must be done. It also restores the natural minerals in the water. There are a huge amount of guides on the internet for a more detailed explanation on cycling your aquarium, and why you should do water changes.

Cycling the aquarium before adding your fish is the single most important thing you can do. Please research further into how exactly you can achieve a fishless cycle.