when I have my Jandy valve right in the middle splitting the skimmer and main drain inputs I get a lot of bubbles in the pump basket. If I close the main drain the bubbles will subside And clear right up. How would I go about troubleshooting and seeing if I have a problem with the main drain lines? Thanks for any input I can maintain a steady pressure in my DE filter but it doesn't stay totally clear when I have it half-and-half.