partial Campden tablets to remove chloramine ?
 

I know 1 campden tab is supposed to remove chloramine from 20 gallons, so if I'm using 10 gallons should I use 1/2 or if I use 30 gallons, 1.5 tabs ??

Do I need to measure the tablets based on the amount I'm using ??

Cut them in half, quarters if your picky, and go from there

Unless someone is allergic, more than you need won't do anything. I just break a chunk off the tablet with my fingernail, more than enough for the batch. Wine makers use way more.

That's for 3 mg/L chloramine as chlorine. If you water contains less you need less and if you are treating less water you need less. Fortunately, it's easy to tell when you have used enough. The water stops smelling of chlorine.

I usually recommend crushing one tablet in the bottom of a glass and dissolving/suspending in a little water. Add some of this to the water to be treated, mix it in and let it sit for a minute or so. Now agitate the water. If you smell chlorine you need to add more of the tablet mix. If you don't or if you smell sulfur dioxide you don't need to add any more.