How much Potassium (or sodium) metabisulfite to remove chloramine?

I have a small jar of powdered Potassium Metabisulfite and Campden tablets that are Sodium Metabisulfite. The tablets are 550mg. I have seen on this forum that these chemicals, when added to your brewing water, dechlorinate and remove chloramine. But how much? I have seen that one tablet does 20 gal but I have to imagine that one tablet's mg content can vary. The Potassium is in powder form, how much of that ought to be used? I am an all grain brewer and I brew 5 gal batches starting with about 7-8 gal. My question: If I used the Potassium, how much should I use? If I used the campden tablet (550mg), should I use a whole tablet or half? I do realize that this has been answered (sorta), but I need more specifics.

Thanks.

Topic campden homebrew

Category Mac

1
answered at

AFAIK, the tabs are standardized. One tab has enough sulfite to treat 20 gal. of water, so 1/2 tab is enough for your needs. If the tabs are are 550 mg., I'd base the powder measurements on that. It would be easy to add a dose of powder and either smell or taste the water to see how effective it was. BTW, water guru Martin Brungard has recently written that excess sulfite will scavenge O2 from the water. That may or may be be a concern. If you use sulfite pre boil, as most people do, should be no problem. Some people use it on their top off water, which could lead to issues with the yeast not having enough O2, although it appears you have to really overdo it for that to be an issue.

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