I would not swim with chlorine levels that low. With a CYA of 65 (which by the way is high enough--I would take the tabs out of the chlorinator and switch to plain bleach if this were my pool--the pucks are going to continue to raise your CYA, which in turn raises your chlorine level to maintain), you shouldn't have chlorine levels of less than 5 ppm...ever. If you are losing chlorine that quickly, then there's something consuming the chlorine in the water. In order to kill it off, you're going to need to get up to that 20 ppm dose and hold it there by testing and adding more chlorine as needed until the levels start to hold.

Janet