Partial Water Changes.

Dechlorinators (I assume that's what you mean) remove chlorine, or if you have chloramine in your water supply they split that up into chlorine and ammonia and remove the chlorine part. Some also contain something to detoxify the ammonia from chloramine, and this is what only lasts up to 24 hours - but by that time your filter bacteria should have removed it. The chlorine removing bit does not stop working after 24 hours.
My water company uses chlorine so I use a dechlorinator that doesn't have anything to remove ammonia.

Dechlorinators usually also contain something to bind heavy metals. This is only really important if you have invertebrates as they are sensitive to copper, which this chemical removes.


If you refill the tank with a bucket, add the amount of dechlorinator to each bucket at the dose for 1 bucketful, so the water is pre-treated before it goes in the tank.
It's when you add the dechlorinator straight to the tank that there are differences of opinion. It used to be said that you added enough to treat the whole tank as the water in the tank will contain dissolved organic chemicals (DOCs) which will react with some of the chlorine removing chemical, and you need to make sure enough is left for the chlorine/chloramine in the new water. But others say that only one dechlorinator actually says to do this, and that's Seachem Prime. All other dechlorinators should be added at the dose for the new water only. I have been told off on another forum for saying to add enough for the whole tank volume as someone did this and it made their fish sick.
My dechlorinator is a bit ambiguous. "Add 1 drop for each US gallon (3.8 litres) of aquarium water." I use a bucket and add 2 drops of dechlorinator to my 7.5 litre bucketful. Should I be adding enough to treat the whole tank volume despite adding it to the bucket? I have emailed the company but the reply was very ambiguous as well.

Maybe email the manufacturer of your dechlorinator, telling them how you refill (add to bucket or straight to tank) and see what they have to say.

thanks sue,i
i add 1ml to 9 litres for a measured dose.

I've been dosing at this level (into the bucket, not to the tank) and haven't seen any problems at all.

I have moved this thread here from General Guidance as that is to explain how to use the Review section.