Water conditioner dosing calculator
How much dechlorinator do you actually add? Enter the water you're treating for the exact dose of each conditioner we review — worked out from the manufacturer's own rate, not a guess.
Dosing a whole tank on setup? Use the full tank volume. Dosing a water change? Use only the volume of new water going in. Every dose here is the maker's own stated rate.
Tank volume vs. water-change volume
The single most common dosing mistake is treating the whole tank on a water change. When you swap out water, you only need to condition the new water going in. Setting up a tank for the first time, or dosing to detox ammonia across the whole system, is when you use the full tank volume. The calculator does the arithmetic either way — you just choose which volume to type in.
Why the doses differ so much
Conditioners are sold at wildly different concentrations, so a bottle that looks pricier can be far cheaper per treated gallon. Concentrated formulas like Seachem Prime treat roughly ten times the water of a basic conditioner per millilitre, which is why we compare on cost per treated gallon, not sticker price. The compare panel above shows the dose gap at a glance.
You can't really overdose most of them
The reviewed conditioners tolerate a wide margin over the label dose, so rounding up slightly is fine — a splash extra will not hurt fish, plants or the biofilter. When in doubt, follow the dose printed on your own bottle, since formulas change. See the full water conditioner rankings for the trade-offs.
Source
- Each product's dose is taken from the manufacturer's stated concentration on the label.
Common questions
How much Seachem Prime for a 20-gallon tank?
Prime doses one capful (5 mL) per 50 US gallons, so a full 20-gallon change needs about 2 mL. The calculator gives the exact dose for your volume and chosen conditioner from each maker's own stated rate.
Can you overdose water conditioner?
A moderate overdose of most dechlorinators is harmless, and Prime is safe up to about 5x for emergencies. Still, dose for the water you are actually treating rather than guessing.
Do you dose for the whole tank or just the new water?
For a routine water change, dose for the volume of new water you add. Dose for the full tank only when treating the entire volume, such as neutralising an ammonia spike.
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