What does the pressure gauge on the filter mean?

It is a useful tool to mainly detect flow issues due to a dirty filter (high pressure) or a clogged impeller (low pressure).  The first and most important info to know about the filters gauge is the clean running pressure. Once that is established, then generally 5 to 10 lbs. of pressure above the initial clean pressure means the filter is dirty. Lower pressure below the initial clean pressure indicates a possible clogged impeller or even a full pump basket.  Call the store for more detailed information.