A little background first is in order... We have an inground 22,500gal w/SWG, sand filter and a vynil liner and are located outside Nashville, TN.
Last year we converted to a SWG and had the best experiance ever!!! Highly recommended! Our costs were minimal and our testing barely wavered at all.
However, this season is another story... we started out with good readings and proper levels all around until recently. Over the past few weeks we have had little to no free chlorine and a combined chlorine of 3 reducing to around 1 in the past week. We have tried shocking with a non chlorine shock at high doses to break the mythical barrier as well as a chlorine shock at high doses of over 10 lbs at a time. The water gets a bit of foam on the surface and you get the idea that something is happening but the next days testing always resulted in a very low FC reading. Just as a note we are treating for phosphates as we had a high reading early in the season but now it's just a maintainance dose. Then we tried cleaning the sand filter now twice, thinking that maybe the problem is in the sand... and last night went straight to 10 bottles of chlorine bleach at 6%. This resulted in alot of fine bubbles and we thought that maybe this was it, placed the robot cleaner in to not only move the water around, but continually brush the walls. A few hours later my wife tested out of curiosity and had a reading of 5 FC and 5 TC which would give us a CC of 0.
This morning her readings were 0FC - 1TC ...
What should we do next, replace the sand; more chlorine ... Help please!