What pressure to backwash sand filter with DE

Notauser

Member
Jun 3, 2020
23
Gainesville, GA
Pool Size
25000
Surface
Plaster
Chlorine
Liquid Chlorine
So I aerated my pool for the first time last week to raise my pH. I used an old backyard pond pump for 13 hours straight, but when I turned it off there was an excessive amount of dirt in the pool that wasn’t there before. I thought that was odd but maybe the aeration caught extra dirt from the air. The deep end was much worse than the shallow end, so I vacuumed it to waste, but the rest of the pool I vacuumed normally. The pool wasn’t cloudy, but you could tell when looking in the deep end it wasn’t crystal clear like normal. So I’ve ran the pump 24/7 for three days now. The water is balanced and passed an ONCLT, just to make sure there’s nothing blooming.



When I brush the pool now, there’s a fine dusting of dirt over the entire pool. So thinking this dirt is too fine for my sand filter (since it’s been three days now and it seems to be distributed evenly over the entire pool) I added some DE to my filter today which leads to my question. I’ve read where you add DE until you get a 1 psi increase in your filter pressure, which took 1 3/4 cups for my 50 lb filter. And I’ve read, where you backwash your filter when you get a 25% increase in pressure. But since I’ve added DE, should I backwash when my filter gets 25% higher than my before DE pressure (10.5 psi) or my after DE pressure (11.5 psi)? I know the difference between the two is minuscule, but the Devil is always in the details. The sand is new as of this year.



Another question I have is, after backwashing a sand filter with DE added, how much DE do you have to add again? I know I could go through the process again of adding 1/4 cup then checking the pressure, but I didn’t know if anyone had any experience on a percentage that seems to work. I read where someone said they added about 80% of their initial dosing after backwashing and it seems to work out. Anyone have any experience with that?
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
16,571
Evans, Georgia
Your filter is a 300 pound filter, same as mine.(see pic below for chart). That DE sure makes the water sparkle!

I'd backwash at 11.5 PSI myself.
 

Notauser

Member
Jun 3, 2020
23
Gainesville, GA
Pool Size
25000
Surface
Plaster
Chlorine
Liquid Chlorine
You are right. I just copied the specs right off of Hayward's website, but the filter weighs 48 lbs empty. It takes 300 lbs of sand, guess the six 50 lb bags that it took to fill it up should have tipped me off. How much DE do you have to add after each backwash?
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
13,541
Houston, Texas
Since you are using DE in a sand filter there are no grids to coat like in a DE filter. All the DE will backwash out when cleaning the sand filter. I would add back the same amount of DE I used before.
 
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