Sand/Salt system notifying low pump pressure and shutting off

Hi,

I have an Intex Sand/salt pump system. I am having trouble with it running correctly. It will run for about 20-30 minutes and then beeps that it has low pump flow and shuts off. I backwash it and rinse it and then it will run again for 20-30 minutes again and continues to shut off. So, I am wondering if its something with my sand? I just got it last year, but should I change out the sand and see if that is the issue? Also, wondering if I am backwashing it correctly… do I keep the valves open to the pool where the water runs back into the pump and pumps out? Or should I be closing the pool water valves before backwashing and rinsing? Thanks so much for your help!