I use k-meta at every other racking. I don't have an so2 meter, but I have a goal of approx 50 ppm of sulfite, so I guestimate it by adding one campden tablet per gallon at every other racking.
I rack whenever I have lees that are 1/4 inch think, or at least every 60 days if there is a dusting of lees. I wouldn't rack in less than three weeks, though- but anytime after that when the lees are thick, or whenever there is even a dusting if it's been a couple of months.
Broken Leg Brewery
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