How much ammonia do I need?

I’ve got back into fishkeeping after quite a few years, and this is the first time I’ve ever cycled a tank with ammonia. My 60 l aquarium has finally cycled but the fish I want are on order at my local aquatic shop. How much ammonia should I add to my planted, cycled tank daily until my fish arrive, please?

LOUISE G, VIA EMAIL

NEALE ADVISES: The exact amount of ammonia doesn’t matter enormously, with different people recommending different amounts. Anything from 0.5 to 4mg/l will do the trick, and towards the higher end, the speed of the cycling process should be faster. For some reason it doesn’t seem to always work that way, so something around 2mg/l is probably ideal. That’s a lot more than fish will be able to handle, of course, but your plants shouldn’t mind. Furthermore, your plants will be bringing in plenty of ‘good’ bacteria with them on their roots and leaves, so with any luck everything should work out very smoothly.

However, adding ammonia doesn’t exactly replicate the conditions needed for the full nitrogen cycle. In the real world, there are four basic steps to the nitrogen cycle: nitrogen fixation, ammonification, nitrification, and denitrification. Put another way, the first step is turning nitrogen gas into ammonium ions that plants can use.

The second step is the breakdown of dead animal and plant material into ammonium ions. The third part turns that ammonium into nitrite and then nitrate ions. Finally, denitrification is the conversion of nitrate ions into nitrogen gas. In fish tanks, all four steps happen to varying degrees.

It’s ammonification and nitrification we care about here, because both of these are how wastes are broken down and processed. Ammonia added to the water provides the nutrients needed for the bacteria responsible for nitrification, sometimes called nitrifying bacteria. So, we’re good there. But what about the ammonification part that precedes it, whereby animal and plant waste is