Can I use solar panels to heat my pool?

Yes. However there will be a fluctuation of temperature due to the daily variation in solar energy. You should run the filter pump and therefore the solar panels from dawn to dusk to maximise the available energy. You should cover the pool at night to reduce heat losses and have a system that is controlled by differential temperature to prevent the panels acting as a radiator at night. If you want to have a more regular temperature in the pool then combine the panels with another form of heating to keep the base temperature in the pool.