[MotoSook]

I have an in-ground and indoor pool. I have a bit of a mystery that my preliminary Google search hasn't turned up any potential cause or solution.

Last year I had a problem with the sand filter multi-port valve leaking. To fix it I had to cut the old PVC pipe off and re-plumb with new PVC.

But before I go further let me add some history. The pool liner was replaced before we bought the house. That was about 3 yrs ago, so the liner is probably no older than 4 years old. After the first winter, I noticed the liner was bunching up in certain areas. The liner was not coming off the wall, and it was not bubbling. Just wrinkling. I thought that was odd and figured the liner was just too loose on initial install since it isn't pulling away from the perimeter of the pool.

We have well water that is considerably hard with H2S which we treat to eliminate the H2S and that smell. Because of the hard water, the alkalinity in the pool water is always high, but I keep the PH and Chloride level in the safe range according to the test strips.

After I fixed the leak last year everything worked fine until the PVC pipe started to deform. The span of the PVC isn't long, and I used plenty of fittings to make the connections, so I can't blame span for the drooping that the pipe developed. The pipe eventually droop/deformed enough to twist the multi-port valve off the sand filter housing. Even the fittings were deforming. It was toward the end of the season last year, so I just said screw it. I though maybe the Chinese made PVC I got from Menard was to blame. This is regular PVC, schedule 40.

So about about 10 days ago, I installed a new sand filter, new sand and new PVC plumbing. I bought PVC from Home Depot this time, Eagle, IIRC, made in the US.

Everything seemed to be fine, and I ran the pool 24/7 for almost a week after shocking. The pool temperature was about 60F, but I ran the heater during those 5 days. Eventually the water got to 80-84 degrees F and the water cleared up.

The last few days we've run the pump to cycle the water and during swimming.

3 days ago, I went swimming with the kids and turned the pump on. Didn't notice any drooping of the PVC. 2 days ago, the pool didn't run at all.

Last night I was on my way home from work and called ahead to have the kids turn on the pump. I didn't go check on it when I got home, but after dinner one of the kids came down to my shop to tell me there is a puddle of water in the pool room. I go to find that the pipes drooped and pulled a couple connections loose and water was spraying everywhere.

The water temperature isn't high enough to soften the PVC, and other than high alkalinity and high Chlorine from the shocking, I cannot figure out what is causing the PVC to soften.

Has any pool owner experienced this?

Any chemist or Chem E have ideas? PCV should not react with the level of chlorine in the pool water. What else could be causing a chemical reaction?

The pump, filter and heater are in a small "closet" within the pool room, but the temperature in there isn't so hot that I expect to see PVC soften. The old PVC seems fine, but all the new fittings and pipe are affected.

Solve my mystery! Please.