Have you kept track of the amount of dichlor you've already added? Each pound of dichlor should add about 11ppm CYA to your pool. no need to test for CYA until you've added about three pounds.

You do need to keep your FC higher, letting it fall to 0 invites an algae bloom. Please review Ben's Best Guess Chart; it provides Free Chlorine target ranges for varrying CYA ranges. Never let the FC fall below the minimum for you CYA.

If you've used less than a pound of dichlor then you should be in the first target band(0-10). When you've used about a pound of dichlor, start targeting the second band(10-20) and when you're into your third pound, move to the third band(30-50).

Test your FC and pH as often as you can at the beginning, the sun will burn off FC fast in a pool with little CYA. Be sure to keep an eye on pH as dichlor will cause it to fall (add Borax when it gets to 7.0).