Anna's right, I would shoot for around 30-40 at first, but only add about 1/2 the dose, then test in 4-5 days, and add more if you need it. CYA is one of those levels that you want to sneak up on, not overshoot and have to drain water! Once you get to the 30-40 range, see if you're able to maintain adequate chlorine levels through the day. If not, you might need to increase it a little, but the bottom line is that the "right" amount of stabilizer depends on your pool. I do keep mine in the 80-90 range, but I'm in a very hot, humid climate with full sun on my pool all day. Without that high level, I can't keep chlorine in the pool--but the down side is that I have to maintain higher chlorine levels than those with lower CYA in order to keep my pool clear. It's a tradeoff.

Janet