When you purchase a new aquarium you can not immediately put fish into it. To do so will induce a protracted and cruel death for any livestock.
Instead, you have to cycle your tank, which involves ensuring your aquarium is full of beneficial bacteria (Nitrosomonas) which can break down ammonia/NH3 (generated by fish poo, uneaten food and other detritus) into nitrite/NO2.
Subsequently, other beneficial bacteria (Nitrobacter) can break nitrite down to nitrate/NO3, which isn’t as toxic to fish as the previous two chemicals and can be taken up by plants.
This near-virtuous circle (you’ll probably still have to do water changes to dilute the nitrate build-up) is known as the nitrogen cycle. But to get it up and running takes some patience – up to a month.
I use an aquarium test kit to track the water parameters of my aquarium. The test kit is from NT Labs and it tests for the aforementioned chemicals that make up the nitrogen cycle (ammonia/NH3 > nitrite/NO2 > nitrate/NO3) as well as pH (acidic to alkaline), Carbonate Hardness/KH, and General Hardness/GH.
Living in Glasgow, Scotland means my tap water is very, very soft, with near zero KH and GH. Thus, to provide some buffering in pH swings, I have to add a KH booster (from Arka), and do so up to a value of 3 or 4. For GH I use Seachem Equilibrium
Below you can see a graph of these water parameters, and from mid-October 2025 through to November you can see the nitrogen cycle running its course.
Imbed with custom width & height + Scrolling enabled
Links
The (almost) Complete Guide and FAQ to Fishless Cycling
