I'm trying to figure out how long to filter my pool each day.

I need my gallons per minute GPM, but my filter has *two* numbers -- the filter tank says 25 and my filter head says 75. They are different manufacturers.

Any idea?

Umm, not really, but I believe I would try to keep apples with apples, and oranges with oranges. You may cause damage somehow and not filter any gallons at all.