If you had a 4 ppm chlorine loss while the sun was off the pool, then you're still fighting something in your water and need to keep it at your shock level for a little while longer. It needs to stay at shock level, as consistently as possible, until you're losing no more than 1 ppm overnight. Unfortunately, if you drop the chlorine level enough to let the kids swim, you're going to lose ground, because shocking to kill stuff in the water depends on SUSTAINED high chlorine levels. Besides, if your chlorine in the water is busy fighting something else, then it can't work on viruses and bacteria in the water, so it's really not clean enough for the kids to get in, anyway.

Keep the chlorine level up, the filter running and backwashed as needed, and it will clear up--it will just take a good-sized dose of POPP--pool owner patience and persistence!

Janet