Campden tablets

When treating water with a campden tablet i normally crush one and add smaller amounts of one tablet to the various waters strike/infusions/sparge. I am wondering if this is necessary.

Is is sufficient to add one tablet to the strike water (1 tablet being enough to treat 20 gallons apparently) and any subsequent water additions will be treated by the excess tablet in the strike water?

Or am i right to add at each stage?

Ta.

You use it to get rid of chlorine or chloromine, I use 1/2 a tab for 30l of strike liquor and 1/4 tab for mash liquor, both amounts being more than enough, but I've forgotten how much 1 tab will treat.

the number in the back of my head is 50l, 1 x campden tab will treat upto 50l of brew liquor..

It would be better to weigh all of your water out the night before in one batch then add a crushed tablet to that. I don't know the contact time to remove chlorine, but I'd safely assume it's not instant, so at least 20 mins - 1 hour would be better. It's wise to remove it - water supply will change from time to time and if you pick up chlorine, it's a dumper.

As Rob Said treat all the water in one go. The 'excess' sulphite will react with chemicals in the mash, its a strong antioxidant, so won't be available 'downstream' so to speak. Technically the reaction is not instantaneous, but add the crushed tablet to the container and then fill it with water, by the time you are ready to use it it will have done it's magic.

1 Campden Tablet will treat 20 US gallons of water or about 17 UK Gallons, don't worry about any excess sulphite it's an antioxidant, so is beneficial anyway.