So I've only just moved into the house in September. I was able to run my de filtered pool last year with no problems whatsoever. Didn't get a lot of time with it at that time. Now here I am now at the beginning of the summertime and we had our pool opened by a company. Ever since we've opened I've been having problems where there's air getting into the pump basket and the pressure in the filter rises quickly with a decrease in return jet pressure. I've been back and forth with the company, after replacing a drain plug that was leaking a bit the company is now saying that I should replace and get a new sand filter. I've literally tried everything I can think of. I've backwashed/cleaned(didn't do an acid-wash/filter cleaner) the grids with hose taking apart the assembly, which helps for a very short time. I've checked to make sure there are no air leaks on any of the fittings. We've narrowed it down that its a problem with the filter as I've put it into bypass mode and there's not a single air bubble that gets into the pump. My filter is a Hayward DE2420. Its at least 13 years old, not sure of exact age. I'm trying not to replace the filter if I don't have to but it's looking that way. Can anyone give any guidance?