I replaced all the water in my pool last weekend. I then put in metal control liquid as directed (waited) 24 hrs then put in concentrated clarifier waited 24 hrs. Then I put in oxy plus as directed. I just can't get the chlorine level up. My pool is crystal clear, but has no chlorine. I have 4 -3 inch chlorine tabs in the pool and still no chlorine. My pool holds 3500 gals. I have also backslashes it 5 times and vaccumed it twice. What to do?