We just built an in-ground pool this year, but before that, I used various above-ground pools. We started with 10' round and finished with, I think, 15' or 16' round. We never used anything other than chlorine/bleach and baking soda, and the water always looked good as long as there was chlorine in the pool. I did later switch to using a spa floating container with 1" stabilized chlorine tablets -- that was actually much easier and less messy than dealing with bottles of either chlorine or bleach. Never had an algae problem unless I didn't stay on top of the chlorine level. It was easy to remove the floating container when we swam, then drop it back it when we were finished.