Filter Pressure Is Reading High After Cleaning.

I have a Pentair D.E. FNS60 that after cleaning and recharging the pressure was at 19 but after running for about 15 minutes will go up to 30 and I will lose suction.
There are also some bubbles in the pool pump basket, but I can't find an air leak. I checked the o-ring on the filter lid and it looks fine.
This may sound stupid but there are 3 pipes that I am told use to run to the pool heater that was taken out. They are not capped at all, could they be letting air into the system?

Thanks for any help you can give.

Justin

Is the pool full of algae? *LIVE* algae will plug a DE filter in minutes; kill it first!

If you don't have high CYA, adding 4 gallons of PLAIN 6% chlorine bleach, each evening, till you can hold a DARK yellow OTO (yellow drops) reading overnight should do it.

I do have some algae so I will give your info a try.
Do you have any idea if those uncapped pipes could be causing the air bubbles I am seeing?

Thanks for the help.

Justin

Air bubbles are usually caused by suction leaks, but fully open pipes on the suction side usually leak so much air that that you lose prime instantly, rather than having bubbles in the water.