Dosing & Chemistry
Ammonia Dosing Calculator
Work out exactly how many millilitres of household ammonia to add to your tank to hit a target ppm, for a safe, repeatable fishless cycle.
Ammonia Dosing Calculator
4 ppm is the standard fishless-cycle target.
Measured with your test kit before dosing. 0 if starting fresh.
Usually 9.5% or 10%. Check your bottle.
Ammonia to add
-mL
- Approx. drops
- 88 drops
- ppm to raise
- 4 ppm
Rough conversion at ~20 drops per mL.
How the ammonia dose is worked out
1 ppm ammonia means 1 mg of ammonia (NH3) per litre of water. So the mass of pure ammonia needed to raise the whole tank by a given ppm is simply: mass (mg) = deficit ppm x tank volume (L).
Household ammonia is sold as an aqueous solution - typically 9.5% NH3 by weight, with a density near 0.96 g/mL. To turn the required mass of ammonia into millilitres of bottle product:
mL = mass (mg) / (1000 x 0.96 x (percent / 100))
Worked example
A 100 L tank, starting from 0 ppm, targeting 4 ppm with 9.5% ammonia: deficit is 4 ppm, mass needed is 4 x 100 = 400 mg of NH3, which is 400 / (1000 x 0.96 x 0.095) = 4.39 mL. Round to 4.4 mL using a syringe.
Safety
Pure ammonia is caustic and the fumes are unpleasant. Wear gloves, dose into a bucket of tank water and stir it in rather than pouring directly into the aquarium. Never mix with bleach or chlorine-based cleaners. Store the bottle upright and out of reach.
Frequently asked questions
What is a fishless cycle?
A fishless cycle is the safest way to mature an aquarium filter before adding livestock. You dose pure ammonia into the empty tank to simulate fish waste, then wait for the nitrogen-cycle bacteria to colonise the filter. Once the filter can process 4 ppm of ammonia into nitrate within 24 hours with no ammonia or nitrite remaining, the tank is ready for fish.
What ammonia concentration should I target?
4 ppm is the standard UK guideline and is enough to grow a robust colony without stressing the bacteria. Some older guides target 2 ppm (lighter stocking) or 5 ppm (heavy stocking). Anything above 5 ppm risks stalling the cycle because extreme ammonia levels inhibit the bacteria themselves.
What kind of ammonia do I buy?
Look for a cloudy / soapy ammonia sold as a household cleaner, usually labelled 9.5% or 10%. Avoid scented or detergent-added products - they often contain surfactants that will foul the tank. UK brands like Kleenoff often vary strength; always check the bottle for the percentage listed.
Why does my ammonia not drop to 0 after dosing bacteria?
New filters can take 4-6 weeks to mature even with bottled bacteria. Dose once to 4 ppm, then wait - don't keep adding ammonia. Only re-dose when ammonia and nitrite are both at 0 ppm and you see rising nitrate. Re-dosing too early stalls the cycle.
Is household ammonia safe to handle?
Yes, with basic care. Dilute before handling, avoid contact with skin or eyes, and keep the bottle away from bleach (the combination is toxic). 30 mL of 9.5% ammonia is not a dangerous quantity, but treat it with the same respect as any cleaning chemical.
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