Um, 20 per quart? The instructions on mine say 80 per gallon, and of course that's for fiber. If hypo clear is good for film, then it's good for RC, too. There's residual hypo test kits available, but I woudn't worry about it. The Patterson RC washer has a little hose at one end, and trickles the water over the print. I forget the flow rate, but it isn't like the hose has a meter on it. I think two water changes should be good.