Normal sand filter differential?

TigerFanatic1

Active member
Jun 1, 2019
25
Louisiana
What is the normal differential pressure on a ‘clean’ sand filter? Mine ranges from 17-20. I’m trying to determine if the installer put enough sand in it, because my pool is cloudy and I’m not seeing an increase in differential pressure or visual indication when I back flush.
 

rowiac

Well-known member
Apr 20, 2018
74
Tehama County, CA
It depends on your flow rate (how fast the pump is running). My filter pressure is 17psi @3000rpm when freshly backwashed. I have determined I need to backwash when it reaches 21psi (~25% increase in pressure). Now that everything is working well with my pool, I should only need to backwash it every 3 months or so.
 

Rollercoastr

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May 18, 2016
861
West Bloomfield, MI
I'd say your "range" is an increase. Not a drastic one though. My clean pressure doesn't change.

Have you read anything about adding DE to a sand filter? I'm a fan. My only regret is that the smallest box I could find is more than a lifetime supply for a sand filter owner. I wish I had looked harder for a smaller box, or found a DE filter owner to give me some. Note that doing this too early in a SLAM could mean that pressure could spike quickly and you'll have to backflush.

 

TigerFanatic1

Active member
Jun 1, 2019
25
Louisiana
Rollercoastr: I haven’t added DE yet, as I am very new to pool ownership. I think I may go that way, I am all for better filtration.

Jim: it’s been in service about 1-1/2 months.
 

rowiac

Well-known member
Apr 20, 2018
74
Tehama County, CA
I've been using Fiber Clear cellulose filter media instead of DE in my sand filter. You can get a 3lb bag for less than $20. Biodegradable and not carcinogenic. Adding either of those may increase your filter pressure slightly. I add about a cup and the pressure goes up by about 1psi.
 

duraleigh

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OP (tiger fanatic)

I think you are SLAMing your pool but you don't say that definitively. How long have you been SLAMing? What is your current FC? How often are you returning FC to SLAM value?
 

TigerFanatic1

Active member
Jun 1, 2019
25
Louisiana
Only been SLAMing for 3 days, was just expecting to see something during backwash. Currently have CYA ~37, FC 15.5, CC 0. Been checking FC 3 times a day, adding enough to get me to 17 each time. 15 is the lowest it has been.

Another concern of mine is algae vs. mustard algae vs. dirt. Originally I thought it was dirt, until I hit it with a brush and it gave off a greenish cloud.
 

duraleigh

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I have a much better picture now....Thanks. It is reasonably common not to get too much debris into your filter during a SLAM. Sometimes the SLAM will plug a filter in a few hours and sometimes it may be days. There is no need to backwash until your filter psi reaches 25-30% above it's normal clean pressure regardless of how much time has passed.

Got a pic of your pool water? That would be helpful. Is your filter and pump one unit on a fiberglass base or are they two separate units? I want to know if the filter and pump are matched or if there is a possibility the pump is too big.

Mostly, I think you probably need a few more days to clear up but stay the course. Keep your FC up at SLAM value and brush and vacuum as often as you can.
Another concern of mine is algae vs. mustard algae vs. dirt.
Disregard that. Probably about a 95% chance you have plain ole' algae
 

TigerFanatic1

Active member
Jun 1, 2019
25
Louisiana
The pictures aren’t the best because I had to use the front camera. I could see the deep end better before brushing about 36 hours ago. Brushing ended up pushing most of algae to deep end, instead of scrubbing motion. I did forget to lower the PH before raising the FC, but later added enough MA to lower to 7.

The pump and filter are separate.
 

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duraleigh

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Don't be discouraged when that brushing clouds up the pool. You have to get that debris pushed up into the circulating water so your filter and vacuum can remove it. Brushing also helps the chlorine kill any remaining live algae.

So, I would give your SLAM a few more days and you should see steady improvement eacxh day (slight maybe but steady) If it somehow is still not clear, I would like to know the diameter or gpm of that filter. That's a pretty powerful pump and you can sometimes overdrive your filter. Give it some more time, continue to brush and vacuum. get the sidewalls, too. Keep your FC up. replenishing FC twice daily is now fine at your stage.........I think the end is in sight.
 

duraleigh

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I think the 1-1/2 diameter might be a typo but the SD-80 is, in fact, good for 75 gpm. The pump is just a little too big for the filter in an ideal installation but it is not so big it is blowing debris through the filter. That match-up is fine.

So, Keep on Slammin'! You'll get there.
 

Rollercoastr

Gold Supporter
May 18, 2016
861
West Bloomfield, MI
I've been using Fiber Clear cellulose filter media instead of DE in my sand filter. You can get a 3lb bag for less than $20. Biodegradable and not carcinogenic. Adding either of those may increase your filter pressure slightly. I add about a cup and the pressure goes up by about 1psi.
I'm going to look into that. I should clarify my statement about being a fan of DE. I'm a fan of the results, but I'm not at all comfortable with all of the warnings that come with pool-grade DE.

the pump is just a little too big for the filter in an ideal installation but it is not so big it is blowing debris through the filter. That match-up is fine.
We might want to discuss the idea of ditching that single-speed pump at some point... IIRC Dave, you told me years ago that my pump was probably too large for my system. Since I've installed a VS, I doubt I've run it at full-speed for even an hour. I haven't done the math, but I suspect I've already reached the payback point in energy savings.