Hi, first time post. I purchased a house last year with a 15K gallon in ground pool with solar panels installed on the roof. Last year I noticed what appeared to be sand at the bottom of the pool. I forgot to mention I have a Hayward sand filter. I was busy doing other things and never had a chance to troubleshoot the problem last year. This year when I opened up the pool I had the solar panels turned off for the first couple of weeks until I got the water balanced. At that time there was no sand in the pool. I turned the solar panels on a few weeks ago and the sand showed up again at the bottom of the pool. A few days ago I developed a leak in one of my solar panels so I turned off the solar panels and again no sand at the bottom of the pool. I already ordered the umbrella latteral pipe for my filter thinking that was the problem but now I am thinking that the problem is in the solar panel plumbing. There is no check valve on the solar inlet or outlet so when the solar is turned on and the pump shuts down all the water drains back through the pump and filter and I think this is how sand is entering into the pool. Does this sound possible? Should there be a check valve on both the inlet and outlet of the solar? If there is a check valve on both the inlet and outlet how will water drain from the solar panels when they are not in use. I'm afraid if I use check valves the water will get stagnet from sitting in the solar panels over the summer when they are not used. Any help is much appreciated, thx