Water conditioner calculator
Work out exactly how much dechlorinator to add, whether you're treating a water change or a whole new tank. Pick your product, enter the water volume, and get the dose in millilitres and capfuls.
Updated 22 June 2026
Treating a water change? Enter the volume of new water you're adding. Not sure of your tank or change volume? The tank volume calculator works it out from your tank's dimensions, and our water changes guide covers how much to change and how often.
Results
For doses under a few millilitres, a cheap 1 mL or 3 mL syringe from a pharmacy is far more accurate than a bottle cap. When in doubt, slightly over-dosing a conditioner is safer than under-dosing and leaving chlorine in the water.
How much to use
Pick your product and enter the volume of water you're treating; the dose appears in millilitres and in capfuls. The standard figures come straight from each product's own instructions:
| Product | Standard dose | Stronger dose | Good to know |
|---|---|---|---|
| Seachem Prime | 5 mL (1 capful) per 200 L (50 US gal) of new water | Up to 5× for an ammonia or nitrite emergency; 2× for very high chloramine | Detoxifies ammonia and nitrite, not just chlorine. One capful is 5 mL, and each cap thread is about 1 mL. |
| API Tap Water Conditioner | 1 mL per 75 L (20 US gal) of new water | 1 mL per 19 L (5 US gal) for chloramine | Very concentrated, so doses are small. Removes chlorine and detoxifies heavy metals. |
Standard, chloramine, and emergency doses
Most of the time you want the standard dose, added to the new water at every water change. Two situations call for more:
- High chloramine. Seachem Prime allows a double dose, and API Tap Water Conditioner uses a stronger 1 mL per 19 L (5 US gallon) rate, for water with heavy chloramine.
- Ammonia or nitrite emergency. Seachem Prime can be dosed up to 5× the normal amount to temporarily detoxify ammonia or nitrite during a spike, for example in a tank that isn't fully cycled. Dose for the whole tank volume, not just new water, and treat it as a stopgap while you fix the cause. Our cycling guide and quarantine guide cover when this comes up.
When you need a water conditioner
Tap water across most of Australia is treated with chlorine or chloramine to keep it safe to drink, and both are toxic to fish and to the beneficial bacteria in your filter. A conditioner neutralises them instantly, so you use it every time you add tap water: filling a new tank, and at every water change. Check whether your local supply uses chlorine or chloramine (your water authority publishes this in its water quality reports), because chloramine needs a conditioner that explicitly treats it. Both products here do, at the stronger dose.
From here: work out your tank or water-change volume with the tank volume calculator, plan the change itself with our water changes guide, and if you're treating new arrivals, see quarantining new fish.