We live inMassachusetts and have a 2 year old inground pool. We started opening it this week. We have backwashed with D.E. now 4 times this week, while trying to vacuum up the residue at the bottom of the pool. The problem is that every time I start vacuuming the pressure shoots up after a couple of minutes to 25 psi and the suction is lost. We have added the Spring opening chemicals also and when we run the pump overnight, the same thing happens when I go out to check the pump in the morning, hardly any pressure coming out of the jets and the psi is high again. I have made sure the skimmers are clear and the pump skimmer also.
Please help, I don't know what is causing the pressure to shoot so high so quickly.

On a side note, I've made sure all the connections are tight, my filter unit was throughly cleaned and stored inside all winter.
Thanks

 

Have you disasssembled and thoroughly cleaned the grids?

 

is the water cloudy? is algea present ? what is the startup pressure ?