Do NOT put the CYA in the feeder. Put it in an old sock and hang it in front of your return jet. Give it a squeeze every now and then and it will help it dissolve faster. The powdered granular type is what you are looking for as long as the ingredients say cyanuric or isocyanuric acid. Are you going to add enough to take it up to 40 or only to about 25 and let your feeder take it the rest of the way? (Once your CYA hits 50, you don't want to use your feeder any more or else your CYA will continue to climb and you really don't want it any higher that that.

(Thanks for making the sig.)