Fishless Cycling — Using an Ammonia Solution

Written 2026-10-05

Dose an ammonia solution (a bottled fishless-cycling product) every 3 days — that’s the standard approach. In the Water Kiwoogi simulator, dosing a 60cm tank with no fish every 3 days for 10 doses brings both ammonia and nitrite down to zero on test-kit readings by day 42, finishing the cycle. Dose the same total amount daily instead, and nitrite piles up to a peak of 54.6ppm on test-kit readings and never comes back down, even after 90 days. Skip fishless cycling entirely and drop in 6 neon tetras on day one, and they start dying on day 13, with all 6 gone by day 16.

Why cycle without fish at all

Cycling is the process of growing a bacterial colony in the filter large enough to break down ammonia and nitrite into nitrate. If fish go in before that colony is ready, their waste becomes the only nitrogen source — and fish produce ammonia around the clock while the colony only grows over days. The fish absorb that gap with their own bodies. Running 6 neon tetras from day one with no cycling help at all in this simulator, they start dying on day 13 and all 6 are gone by day 16. An ammonia solution feeds the bacteria directly instead of through a fish, growing the colony without putting any living creature at risk.

Every 3 days gets you there by day 42

Each dose of ammonia solution hands the ammonia-oxidizing bacteria (Nitrosomonas) a batch of food at once. Spacing 10 doses 3 days apart gives the nitrite-oxidizing bacteria (Nitrobacter) time to catch up while Nitrosomonas works through each batch. In this simulator, ammonia peaks at 4.38ppm on test-kit readings, nitrite peaks at 23.69ppm, and by day 42 both read zero and stay there.

Dose too often and it never finishes

Dose every day instead, and the next batch lands before the last one has been processed. Nitrosomonas grows faster than Nitrobacter, so ammonia still gets handled well enough, but the nitrite it produces keeps outpacing Nitrobacter’s growth and just keeps piling up. Dosing the same total amount daily for 30 doses and running it out to 90 days, nitrite peaked at 54.6ppm on test-kit readings and never dropped back down — the cycle simply never finished.

What to actually do

Following the interval your product’s instructions recommend (usually 2–3 days) matters most. If you can, test ammonia before each new dose and wait until the last one reads near zero — spacing doses out matters far more for colony balance than adding more of them. Once both ammonia and nitrite hold at zero on test-kit readings, you can start adding fish gradually. Never dose ammonia solution into a tank that already has fish in it — that’s not cycling, it’s poisoning. If you’re unsure, it’s safest to check with a local aquarium shop or an expert.

The button below runs the 60cm standard tank · ammonia solution every 3 days, 10 doses · no fish tank from this guide. Switch the dosing interval to daily and run it again to see nitrite get stuck for yourself.

The numbers in this guide come from the Water Kiwoogi simulator model; real tanks can differ.