You'd think it'd be obvious, but sometimes it's not!
If you ever go to your pump/ filter and hear a strange noise or see water squirting out of the plumbing --- turn off the pump!!!!!
I had to replace the lines between the pump and filter today because the pool owners son didn't mention a strange noise when he checked the pump a couple of days ago, the noise was the pump starving for water.
The reason for this post is to tell people to shut down the pump system if something is amiss, ask a question here or have the local pool dude check it out - before!! a major problem arises