Filter is losing pressure very quickly -- pls advise

stupidcon

Member
Aug 31, 2016
16
Knoxville/TN
Greetings!

I recently opened my pool, and I'm noticing that my filter pressure is dropping very suddenly.

I did a total sand replacement last season, and I do a pretty good job of getting most debris out of the water before it even reaches the skimmer. I'm noticing that the return jet pressure drops to almost a standstill after about 2 hours of operation, but when I backwash (even for just 5 to 10 seconds), it returns to full force as soon as I start filtration again.

What could be causing this drop in pressure? I was thinking some kind of clog, but I don't know how backwashing for such a short amount of time would consistently clear the clog. I haven't given the pump basket a thorough look as it is below my deck and sort of a pain to get to, but from what I can see it is crystal clear along with my top skimmer basket.

Any advice greatly appreciated. Thanks.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
21,900
San Dimas, CA (LA County)
The filter is working exactly as designed. As it gets full of superfine debris, it clogs and the pressure rises, and backwashing makes it all good again. You've got algae. If it isn't green right now, it will be soon, unless you get ahead of it. That's called a SLAM Process

Things will likely get really bad for a day or two as far as clogging the filter and then the water will start to clear up and the filter will go longer between backwashes as the SLAM progresses.
 

stupidcon

Member
Aug 31, 2016
16
Knoxville/TN
The filter is working exactly as designed. As it gets full of superfine debris, it clogs and the pressure rises, and backwashing makes it all good again. You've got algae. If it isn't green right now, it will be soon, unless you get ahead of it. That's called a SLAM Process

Things will likely get really bad for a day or two as far as clogging the filter and then the water will start to clear up and the filter will go longer between backwashes as the SLAM progresses.

Ok. I am in the middle of SLAM'ing right now. My CYA is close to 0, so I have been aiming for 10-12 PPM FC. I have been using PoolMath and adding the appropriate amount of 10% NaHypo to reach these levels. I will continue to give it time. The pool is essentially clear so the debris must be very super fine and copious for it to be clogging as fast as it is. I will keep at it. Thanks

***EDIT*** is there any harm in me using some extra 99% dichlor I have to help shock in addition to the liquid chlorine I'm adding, considering I have minimal if any CYA in the water?
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
21,900
San Dimas, CA (LA County)
Ok. I am in the middle of SLAM'ing right now. My CYA is close to 0, so I have been aiming for 10-12 PPM FC. I have been using PoolMath and adding the appropriate amount of 10% NaHypo to reach these levels. I will continue to give it time. The pool is essentially clear so the debris must be very super fine and copious for it to be clogging as fast as it is. I will keep at it. Thanks

***EDIT*** is there any harm in me using some extra 99% dichlor I have to help shock in addition to the liquid chlorine I'm adding, considering I have minimal if any CYA in the water?
Use Effects Of Adding Chemicals at the bottom of PoolMath to figure out how much you can safely add. And once you're at 30 CYA, you need to target 12 FC.