I have a half new half old Pentair SMBW 4060 filter. When the pump is running there are no visible leaks. When pump shuts off you can here air coming into filter. It's a slow sputter sound. Slow enough where DE will come back into pool but pump never loses prime.
When pump comes on in the morning of coures there is a big gurgle of air that comes into pool with sometimes a trace of DE through the retuns. Once air purges there is no noticable bubbles through returns.
Have had the bottom of filter, a few grids, and the gasket changed. Any ideas?