The algorithm needed to optimally run a pool filtration pump is:
10 hours/day if water (not ambient air) is at 90 degrees
5 hours if water is at 50 degrees
assuming it's a properly sized pump and it's a single speed pump.
If it's a dual speed pump, and if you're running the pump at low speed, then just double the numbers above. I.e.
20 hours if water is at 90 degrees
10 hours if water is at 50 degrees
You should let pump (filter) 'relax' once half way in between the daily run time, for 15 minutes.
Use this as a guide to see how pool water temperature various as a function of month of year: http://www.welserver.com/perl/plot/WEL0343/PoolWater.png . In my case, I have to run the filter pump 20 hours per day, on low speed, during the height of the summer. Right now I should be running it about 10 hours per day on low speed.
Hope this helps.