Runs well after starting, but hard to start

Hi,
I have an inground pool (an old pool), with a Hayward pump and filter system. The system runs well, after starting, but is hard to start after being off overnight. At such time I have to prime the pump by filling the prepump basket with water, which I've never had to do in previous years. If I turn the pump off after it's running, it starts well. I have over ten years of experience running the pool, so am familar with it basic operation.
Thanks,
..... john

Somehow, air is slowly getting into your pump when it is off. If there are there any tiny air bubbles in the return water, that's a good indication that you have a leak between the skimmer and pump. If you have a water leak between the pump and return, that will let air in when the pump is off. A good place to start checking for leaks is the pump seal. Do you have a check valve in the system?