When/how To Use Dechloriator?

[Raticataticus]

I've always lived at a house with a rainwater tank so I've never used dechlorinator before.
 
Do you have to dechlorinate the water and let it sit overnight or do you just chuck the new water in the tank and then chuck the dechlorinator in. I've seen it done both ways and I'm just not sure.

 

[fluttermoth]

You can either;
 
dechlorinate each bucket as it goes in; you don't need to leave it to stand at all as it works pretty much instantly, just give it a mix or
 
you can add the dechlorinator to the tank, and then add the water.
 
You can add the dechlor after filling the tank, as the amount of chlorine in a 40 or 50% change will not be enough to damage your fish or your filter bacteria, but I'd always add it first (and keep the filters switched off), just to be on the safe side.

 

[Ch4rlie]

Personally I do as Fluttermoth says add dechlore straight to fresh water in the buckets if using bucket method then add bucket water into tank pretty much straightaway, no need to stand the water for any length of time really after adding dechlore.
 
Or if I am using a Python Hose setup, I dose for the whole tank water volume and add that whilst re-filling the tank directly from tap.
 
I am careful to add exact amounts of dechlorinator as I use Seachem Prime and that is pretty concentrated stuff.

 

[Baccus]

Either method can be used, however for delicate or finiky creatures such as shrimp it is better to dechlorinate the water prior to adding to the tank and if possible leave the tub of dechlorinated water to age for a week in the out doors.