Aquarium · Tank cycling
Fishless cycle ammonia dosing calculator
A fishless cycle only works if you're feeding your filter's bacteria a consistent, known amount of ammonia, not a guess. Too little and the bacteria colony grows too slowly to matter. Too much and you can stall the cycle entirely, since very high ammonia is itself toxic to the bacteria you're trying to grow. This calculator converts a target ppm into an exact dose in milliliters for your specific tank size and ammonia solution strength, so you're dosing a number instead of eyeballing drops.
Check the label. Plain household ammonia is usually 5-10%. Pure ammonium hydroxide sold for cycling is often 9.5-10%. Never use a product with surfactants, dyes, or perfume added.
Add to your tank
1.59 mL
- Add this, wait for it to mix, then test with a liquid test kit. Redose to the same target any time ammonia reads back at zero.
- Ammonia fumes are toxic. Dose in a ventilated room and avoid breathing directly over the solution.
What to actually buy
Dr. Tim's Aquatics Ammonium Chloride (2 oz.)
A pure, chlorine-free ammonium chloride solution made specifically for fishless cycling, so the concentration on the label is accurate and this calculator's math actually holds. Avoid scented or surfactant-added household ammonia.
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How this is calculated
One part per million of ammonia in one liter of water is 1 milligram. So the mass of ammonia needed for your tank is just your target ppm multiplied by your tank's volume in liters (gallons x 3.785).
That mass has to come from a diluted solution, not pure ammonia gas, so the calculator divides by your solution's concentration to get the volume of liquid to add. A weaker solution means more milliliters for the same ppm bump; a stronger one means less.
INJAF's fishless cycling guidance targets 2-3 ppm ammonia to kick off the cycle. This calculator defaults to 2 ppm but lets you adjust it if you're following a different guide, like Dr. Tim's One & Only method, which uses a different target.
This assumes your ammonia solution has roughly the density of water, which holds well enough for the dilute household and ammonium hydroxide solutions people actually use for cycling.
Frequently asked questions
What ammonia solution should I actually use?
Pure ammonium chloride or ammonium hydroxide made for fishless cycling, with no added surfactants, scents, or dyes. Regular household ammonia sometimes has soap or detergent mixed in specifically to make it sudsy, which is harmful to the tank and throws off this calculator's math since you can't be sure of the actual ammonia concentration.
How often do I need to redose during the cycle?
Test first, then dose based on what you find. Once ammonia is reading zero on a liquid test kit (meaning the bacteria have processed the last dose), add another dose to the same target ppm. Early in the cycle this might be every couple of days; once Nitrosomonas bacteria are established, ammonia often clears within 24 hours and needs daily redosing.
What if I add too much ammonia by accident?
A large water change dilutes it back down. Ammonia above roughly 5 ppm can start slowing or stalling bacterial growth rather than helping it, so if you've badly overshot, a 50% water change and a fresh test is safer than waiting it out.
Do I keep dosing ammonia once fish are in the tank?
No. Once the cycle is complete and you've added fish, they supply the ammonia through waste. This calculator and dosing schedule is only for the fishless cycling phase, before any fish are in the tank.