Cycling with Fish Pet of the Month
🐶 POTM Poll is Open! 🦎 Click here to Vote! 🐰


Fish Fanatic
Jul 22, 2004
Reaction score
Eglinton, North of Ireland

I am currently cycling my 180litre tank with 5 Mollies. I carry out 33% water changes every second day. My ammonia levels are between 1 and 3 ppm before each water change. No nitrites are being recoreded as yet.

In your experience how long does this sort of cycling last, I presume adding additional ammonia is a no no when fish are in the tank.

As my tank is reasonably large should I add more fish to increase the amount of ammonia being produced? I don't mind carryingout water changes daily if it speeds things along!!!

On a positive note all remaining mollies are doing well (one died after 2 days).
Why add more fish when that will only mean more water changes to keep ammonia down. Just keep the ammonia low by less fish. The bacteria will develop in the same amount of time. You have a fine number, 1 fish per 5 gallons is about right.

Your Ammonia will fall after a while (the time is hard to predict, but for me was about 3 weeks) and the nitrites will rise, that signals that the first stage bacteria are there, and they should multiply to handle more fish quickly. But don't add more fish yet! The second stage bacteria must be in the same position, which is signalled by nitrites falling and nitrates rising. This stage apparently takes longer than ammonia->nitrite, but when the nitrites fall they do so rapidly.

When both Ammonia and Nitrite register as 0 the cycle is complete and you can add more fish. But do so slowly, as every time the bioload increases the filter bacteria have to expand to accomodate the new fish.

Nitrates will continually rise, and can be reduced by water changes :)
Thanks for that.

Once the cycle is completed people recommend a 25% water change every 2 weeks to keep nitrates down, but out of interest what is the danger level for nitrates before fish become ill.

Most reactions


Staff online