I just bought a house in San Diego with a 13k gallon in ground pool. It had a single speed pump which we replaced with an Intellifo VS. Before changing the pump, the pool was always above 80 with just solar heating. Since replacing the pump, it has been closer to 72.
I have played with the rpms extensively. With 240 sqft of panels, it appears 36gpm would be appropriate. Using the spreadsheet from this site looking at rpms and watts, 2100 rpm should pump that. I've tried 2100 with 13psi up to 2400 with 16psi and the water temperature does not rise over 3 days.
I heated the pool to 78 this morning and it has dropped to 74 since then. Outside temp is 89 and the panels have been in full sun.
How can I solve this?