Testing water parameters with the API Test Kit

How to test your aquarium water parameters

Harmful chemicals in the aquarium build up very quickly, here I’ll talk about how to test your aquarium water parameters the most effective way. By water parameters I mean how high certain chemicals are in the water.

We want to test how high certain harmful chemicals are in the tank. To test these, most people use the All In One API Master Test Kit. This kit is very popular, very accurate, and good value for money. Every fish keeper should own one.

Once the tank has been set up a while and the water parameters are stable you won’t have to test the water as often.

When it comes to talking about the chemicals in your water and therefore water parameters it can feel like a lot of effort and a bit daunting. But as I stated above, you won’t need to do much once it’s stable. Checking once a week and then down to once a month.

The most important bit of information is what causes harmful chemicals in the tank. Primarily fish waste, and uneaten fish food. These first turn into ammonia. Ammonia is a harmful chemical that kills your fish, it practically burns them.

The Cycle

To solve this we use a filter. A filter not only visibly cleans your water by trapping chemicals in the sponges (mechanical filtration), it also neutralises the ammonia before it becomes a problem (Biological filtration).

Your filter will build up good bacteria on it’s sponges and ceramic rings. These can hold a lot of good bacteria because of the huge amount of surface area. Once the filter harnesses enough good bacteria to neutralise the ammonia, we then say that the tank has now been cycled.

By neutralising the ammonia, we mean it turns the ammonia into Nitrite, and then Nitrate. Nitrite is also very poisonous to your fish. The Nitrite is then further neutralised by being turned into a smaller amounts of Nitrate. While Nitrate is also poisonous, it’s not as harmful and can be tolerated when at very small amounts. The Nitrate is then used up by plants, and taken out with water changes.

Fishless cycle

To build up good bacteria on your filter sponges without causing any harm to any fish we do a fish-less cycle. Every fish keeper should know about cycling a tank. (Google fish-less cycle and you will see in-depth guides about how to do this.) It’s basically done by adding liquid ammonia to your tank without having any fish in the tank. Once the filter starts changing this liquid ammonia into low levels of nitrate the cycle is complete, and you can add fish to safe waters.

A fish-less cycle will not expose any fish to high amounts of ammonia, resulting in no fish deaths. This is why it is preferred.

The Test Kit

When your test kit starts showing no signs of ammonia or nitrite and only small amounts of nitrate it means the tank has been cycled and is now safe to add fish. (The test kit has instructions and will tell you what the results of your tests mean).

How to test your aquarium water with the API Test Kit
These are my results. 0ppm means there are no signs of the chemical, it’s colour coded for easy readability. I have near 0 amounts of ammonia and nitrite, while I have a small amount of Nitrate. Very good results.

You can help your tank even further by adding plants which will absorb even more of the nitrates.

Make sure not to clean your sponges in tap water because the chlorine will kill all the good bacteria and you’ll have to start the cycle again.

Filter components

Filter sponges

It’s common for filter companies to instruct that you replace the filter sponges with new ones every couple of weeks or so, but this really isn’t the case. They just want you to spend more money.

The only time you need to replace the sponges is when they’re falling apart. All they need is a quick swill (in tank water) to remove any particles.

Ceramic Rings

Ceramic rings are brilliant for biological filtration and will help keep your aquarium water safe.


A lot of the time a new filter will come with a bag of carbon too. Most people including myself will take this bag of carbon straight out. The carbon is only really needed when removing things like medication and tannings from the tank water. It also needs to be replaced often (roughly after a couple of weeks) as the carbon will eventually become inert.