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Ammonia Dosing Calculator (Fishless Cycle)

For fishless cycling with pure ammonia (no surfactants, detergents or added scent). Always confirm your ammonia is pure with a shake test before dosing.

Your numbers
2 ppm is a commonly used fishless-cycling starting target
Check the bottle — household ammonia is often 5–10%

Dose in small increments and retest

Dose in small increments and retest rather than adding your full calculated amount at once the first time — it's much easier to add more than to remove excess.

How this dose is calculated

The math converts your target ppm (milligrams of ammonia per liter of water) into a total milligram amount for your tank's volume, then works out how many milliliters of your specific solution strength delivers that amount, using the solution's concentration and an approximate density for dilute ammonia solutions. This is a from-first-principles calculation, so it adapts correctly to whatever concentration your specific bottle is labeled at — always enter the actual percentage from your label, not an assumed one.

Why 2 ppm and not higher

Older fishless-cycling guidance often suggested 4–5 ppm, but more recent guidance from bacteria-culture researchers suggests very high ammonia concentrations can actually inhibit the nitrifying bacteria you're trying to grow. A lower starting target around 2 ppm, maintained consistently, is now more commonly recommended.

Confirming your ammonia is safe to use

Only use pure ammonia with no surfactants, detergents, added scent or coloring. Shake the bottle: if it foams or bubbles persist, it likely contains a surfactant and shouldn't be used. Look for "ammonium hydroxide" or "ammonia" as the only listed ingredient.

Source: The 2 ppm starting target reflects fishless-cycling guidance popularized by aquatics researcher Dr. Timothy Hovanec (Dr. Tim's Aquatics), which found very high ammonia levels can inhibit the nitrifying bacteria being cultured.

Frequently asked questions

How do I know my household ammonia is pure enough to use?

Shake the bottle vigorously. Pure ammonia solution will not foam or will clear almost immediately; if suds persist, it likely contains a surfactant or detergent and isn't safe to use for fishless cycling.

What do I do once I hit my target ammonia level?

Test daily and re-dose to maintain roughly your target level as bacteria begin consuming it, watching for nitrite and then nitrate to appear over the following weeks as the nitrogen cycle establishes.

Can I use this same dose once fish are in the tank?

No — this calculator is specifically for fishless cycling with no livestock present. Never intentionally dose ammonia into a tank containing fish.

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