This is pretty long winded but here it goes. Our pool seems to be in a "chlorine lock". Over the last 2 weeks we have added close to 60 pounds of shock and FC and TC are still at 0.5 we were told that something was eating up the chlorine and they tested for the dreaded phosphates which came up at 3000! We treated with phos free and 48 hours later we back washed our pool and cleaned the de filter then added 5 pounds of shock. For the first time in 2 summers we held the chlorine but only for about 36 hours then it was back down to 0! We shocked again and it held again for only a few hours. Phosphates were retested and they are at below 100. What now??????