Dechlorinater Dosage

Hi all, I've just carried out a 30% water change and I have a query regarding the dosing of dechlorinater. Should I be dosing with for the amount of water changed or for the total volume of water in the tank. I've dosed for the 30% this time but want to know the right amount for next time.

For those who want to use a hosepipe, or the dosage amount makes it difficult to measure the amount for a bucketful, you can put the whole dose in the tank then add the water undechlorinated.
I always add the right amount for a bucketful into each bucket of water.





It used to be said that if you add dechlorinator to the tank then add water you had to add the amount of dechlorinator to treat the whole volume. This was because one brand of dechlorinator had it in the instructions and everyone assumed it was the same for all brands. It isn't.