Fishless cycling ammonia dose calculator
Enter your tank's real water volume and the ammonia strength printed on the label. You get a starting estimate for the dose, the half-dose to add first, and how much to top up from today's test reading.
Result
About 4 ml for 2 ppm
Your first dose
- Add about half, 2 ml, measured with a syringe kept only for ammonia.
- Wait until the filter has mixed it through the whole tank, then test.
- Scale up. Ammonia rises in proportion to what you add, so if 2 ml gave about 1 ppm, about 4 ml in total gives about 2 ppm. Add the rest in one or two steps, testing as you go.
- Write down the total that gave about 2 ppm. That is your full dose for this tank; enter it above for exact top-ups.
Topping up
At 0 ppm, add about 4 ml to bring it to about 2 ppm. This uses the label estimate; once you know your measured full dose, enter it above.
Some labels give the strength as ammonium hydroxide rather than ammonia. Then this estimate can come out low, which errs on the safe side. Add in steps and let your test kit have the final say.
Handle ammonia with care
- Use pure ammonia sold for fishless cycling, or plain household ammonia with no scent or surfactants.
- Wear gloves, open a window, and keep it in its original, labelled bottle, away from children.
- Never mix ammonia with bleach or other cleaners: together they release toxic chloramine gases.
How the calculation works
2 ppm means 2 mg of ammonia in every litre. If the label gives the ammonia content as a percentage, each 1% is about 10 mg per ml. So ml ≈ target ppm × litres ÷ (label % × 10), and a top-up is ml ≈ full dose × (target − reading) ÷ target. These are the formulas in our fishless cycling guide. They agree with the SRAC biofilter fact sheet's example: 60 ml of 10% ammonia raises 3,785 litres by about 1.6 mg/L.
Getting an accurate dose
- Use the real water volume. Gravel, rock and the gap below the rim take up space, so work it out with the aquarium volume calculator.
- Dose against your test, not the bottle. Most test kits read total ammonia in mg/L, which is the same as ppm.
- Test your treated tap water too. Chloramine-treated water can carry some ammonia, which would confuse later readings.
- Keep a log. Write down every reading and every ml you add. The fishless cycling guide has a day-by-day testing log and what to do if the cycle stalls.
New to cycling? Start with how to cycle an aquarium. When it is done, add a few hardy fish first, such as those on the beginner fish list.
Common questions
How much ammonia do I add for a fishless cycle?
Aim for about 2 ppm, which is 2 mg of ammonia in every litre. If the label gives the strength as a percentage, each 1% is about 10 mg per ml, so ml ≈ 2 × litres ÷ (label % × 10). For 5% ammonia in 100 litres that is 4 ml. The US Southern Regional Aquaculture Center's example agrees: 60 ml of 10% ammonia raises 3,785 litres by about 1.6 mg/L. Add half first, test, then build up.
What kind of ammonia should I use?
Pure ammonia sold for fishless cycling, or plain household ammonia with no scent or surfactants. If the product is sold for fishless cycling, follow its label. If the label gives no strength, skip the estimate and start with a few drops.
When and how much do I top up?
Top up whenever ammonia falls below 1 ppm, back to about 2 ppm: top-up ml ≈ full dose × (2 − reading) ÷ 2. At 0.5 ppm that is three-quarters of your full dose; at 0 ppm it is all of it. Test again before topping up if you have just changed some water.
What if I add too much ammonia?
A water change brings it down. If your treated tap water has no ammonia, changing half the water takes 4 ppm to 2 ppm. Some chloramine-treated supplies carry a little ammonia, so test your tap water too.
Is ammonia dangerous to handle?
Handle it with care. Wear gloves, open a window, and keep it in its original, labelled bottle, away from children. Never mix ammonia with bleach or other cleaners: the New Jersey Department of Health warns that together they release toxic chloramine gases.
When is the cycle finished?
When ammonia and nitrite both read 0 ppm within 24 hours of a 2 ppm dose and nitrate is rising, usually after 4–8 weeks. Then do a large water change and add your first few fish.
Sources
More tools
Keep your tank's tests, water changes and costs together in AquaLog.