10 PSI over normal before backwash?

bassadict69

Well-known member
May 26, 2007
148
Benton, La
#1
It is said over & over again not to backwash a sand filter until the pressure is about 10 psi over the normal reading. With mine, at just 4-5 psi over normal, the water doesn't seem to be flowing into the skimmer very well & the water in the skimmer is barely moving & dust, dirt, etc. is floating on top of the water in the skimmer. Is that normal or should I go ahead & backwash?
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
#2
Go ahead and backwash if you want. There is no fixed rule about 10 psi over, some people do 6 psi or 8 psi, some people go a week or a month. Do whatever works for you. The main down side to backwashing too frequently is that you lose water every time you backwash.
 

bassadict69

Well-known member
May 26, 2007
148
Benton, La
#3
Am I correct in thinking that when the water looks stagnant in my skimmer that it is probably not filtering well even though it still seems to have a good flow out the return?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,181
Pleasanton, CA
#4
One thing to remember is that 10 PSI is 23 feet of head so if you wait that long, you will be reducing the flow rate of your pump by quite a bit. I would backwash well before 10 PSI and probably before 5 but you have to balance that with how often you would be doing it. A backwash every couple of weeks at 5 PSI is reasonable while every week many not be. There really is no hard and fast rule but I do think 10 PSI is too high.
 

Aquaman95

Well-known member
Feb 20, 2008
249
#5
5-10 psi is the general rule for commercial pools, but commercial pool filtration systems are supposed to be sized so they achieve correct turnover *with* a dirty filter. It doesn't always work out that way though.

I usually recommend backwashing as little as possible but don't exceed 10 psi. If the filter system isn't achieving good flow at a lesser PSI then that's when you need to backwash.

The main reason is that a sand filter with some dirt load will filter better than a clean filter. Water waste and *possibly* wearing out the sand quicker is also an issue but that last one is somewhat debatable.
 

tnthudson

LifeTime Supporter
Mar 31, 2008
328
Central VA
#6
Aquaman95 said:
The main reason is that a sand filter with some dirt load will filter better than a clean filter.
Cool, I had heard this before. I usually wait until 10 psi over the starting pressure, but after my BBB conversion early this season, the filter won't go any higher than maybe 4 psi over its' starting point. So before vacation I backwashed, but haven't really had to in weeks since then. Is that normal with new sand?
 

Aquaman95

Well-known member
Feb 20, 2008
249
#7
Yes, that can be normal with new or even old sand. Those pressure gauges can get clogged but as long as you see movement out of it and it drops to 0 when you shut the system off the gauge should be fine.
 

chatcher

LifeTime Supporter
Jun 7, 2007
62
Raceland, Kentucky
#8
bassadict69 said:
Am I correct in thinking that when the water looks stagnant in my skimmer that it is probably not filtering well even though it still seems to have a good flow out the return?
Check to make sure the weir (floating flap) on your skimmer is present and moving freely. If it is missing or stuck down (not floating), the water in the skimmer will look abnormally still even if the flow is normal.