PSI gauge climbing quicker than normal DE filter, Pentair FNS Plus 48sqft


Bronze Supporter
May 3, 2016
Collinsville, IL
I backwashed on 6/4/2020 and today 6/8/2020 my PSI has increased from 8 to 11, run my pump at 2100RPM. Normally, it does not happen that quickly so I am a little concerned. We did have a busy weekend in the pool this past weekend but I would not think that would cause such a quick increase.

I have a 48sft Pentair FNS DE filter and I normally put 10 scoops (Aladdin cup) when backwashing. Could the cause of the increase be due adding too much DE when recharging? I have always added 10 scoops after backwashing and never had this issue. Pool company told me to always add 10 scoops but after researching I think I should be adding around 8 (80%) scoops after backwashing. They literally said, "Always add 10 scoops after backwashing" when I told them I read to add 80% of what you normally start with which would be 10 scoops.

I noticed a change in water flow to both of my skimmers, mainly the shallow end skimmer, perhaps due to it be furthest from my pool pump. Normally, there is a good current flowing in both of them but now there is little coming into the shallow skimmer and a weak one in the deep end skimmer. When I notice this along with my pressure gauge getting high, I backwash which fixes the issue and my water flow is normal again.

Should I backwash again and only add 8 scoops to see if that fixes the issue?

Below are my test results, just in case it could be a water chemistry issue:

FC = 4
CC = 0
PH = 7.8
ALK = 80
CH = 325
CYA = 60
SALT = 3400
WATER TEMP = 80 degree


Silver Supporter
Aug 15, 2019
North NJ
The owner's manual calls for 4.8 lbs of DE (or ten 1 lb. coffee cans) to properly fill the grids, they don't mention a different amount for back washing. I don't know what an Aladdin cup is so I can't tell you if ten cups is correct or not.

My DE filter is the same size, I add 5 lbs after a full cleaning and 4.5 lbs after a back wash. Not sure if that makes a difference but it works for me.