Hello, all. I'm stumped by this. The pump is running strong, water comes in from the skimmer and the main drain. If I loosen the pressure valve on the DE filter, water spurts right out. But nothing is coming out of the return lines, except a very few bubbles if I've restarted the pump. I would expect the water level to go down if there's a leak somewhere, but it remains even. Any ideas what I can try on my own before I have someone come out and do expensive troubleshooting? Thanks in advance for any help.