Asking for my cousin who just inherited her mom's house and pool. About 25,000 gallon in ground vinyl and 40 years old. No idea the age of the pump or filter (sand). Took cover off pool about 3 weeks ago after almost 2 years. She installed a Hayward SWG and has been working to clear the green swamp. The issue: When the pump is first turned on the water flows fine our of the returns and the swg will come on. After running about 4/5 hours, the flow is so low that the swg won't run and there is barely any water coming out of the returns. She can turn the pump off for a few minutes, and when she turns it back on it works fine again. ?? What do you think she has going on? thanks