The pool is using little chlorine because the water is cold, but when the weather starts to warm up, if you don't run higher cl levels you'll have a green pool! We see it all the time. Since your CYA is 80-90, then you don't want to use any stabilized forms of chlorine. So stay away from trichlor pucks and dichlor powder. What kind of pool is this -- gunnite, vinyl, fiberglass? Also, go ahead and post a full set of current water testing results.