Do this. Test the water this evening. Then, add enough bleach to take the chlorine back up to 20ppm. Tomorrow morning within an hour or so of sunrise, test the chlorine again and post your readings. We are looking for overnight chlorine loss. If you lose no more than 1ppm of chlorine overnight, then you can let the chlorine drift down and keep it between 5-10 all the time. If you drop lower, you risk algae. But, if you do lose more than 1ppm overnight, then you continue to keep it at shock level until you do pass the overnight test.

If you don't use the tablets in your pool, what other uses are you talking about. I'm curious.