Sand filter let's silt through? Alternative media?

Tfastle

Active member
Mar 17, 2014
43
Albq. NM, United States
My pool is about 5 years old and has a cover over it most of the time. Since it was new I have had an issue with silt collecting in areas of the pool. The longer the pump runs the more silt. It's a very fine silt and dissipates with water movement but, of course, settles out again over time. It's sort of a drag when you have people over and you open your pool and it looks like it has debris all over the bottom.
I contacted Jandy (the manufacturer of the filter) and they said no silt should get through the filter and it was likely the wrong sand, broken or cracked laterals or a leak in the stand pipe. Finally, last summer I got tired of it and tore the filter down, replaced all the laterals (although none were damage, replaced all the sand with pool specific silica sand and replaced the stand pipe making sure it fit very tightly. Ah, now more silt. Wrong! Same problem with no discernible change. I read more about filters and, from what I can tell, Sand filters are great because they are so simple and easy (I would concur whole heartily with that) but they only filter down to 20 microns. It seems DE and Cartridge filters filter down to 4-5 microns. I think the rep at Jandy that said there should be no silt is wrong. I am in New Mexico in a dry and relatively dusty environment. The dust here is very fine and I don't think a sand filter can get it all out.
So, my questions are - am I crazy or does this make sense? And, is there a way to get a sand filter to filter this very fine silt out or do I have to switch to a DE or Cartridge filter (other options?)? I have heard and read about adding some DE to the sand or using alternative filter media (glass beads, other). Anyone have any experience with this?
Any thoughts or input would be appreciated cause ... I am sick of the silt!

Thanks!
 

Tfastle

Active member
Mar 17, 2014
43
Albq. NM, United States
Yes, from what I learned here I actively monitor and manage my chems using the test kit recommended here. Use liquid chlorine and supplement with tablets when out of town. The pool has a cover and is covered nights and during the day when not in use. Get very little debris in the pool. I put a silt basket in my robotic cleaner and, after 3-4 cycles it will get most of the silt out but when I run the pool silt returns. As a matter of fact, the only way I have come up with to manage it is to run my pool less. The less the pump runs the less silt I have. When I replaced the laterals, sand and stand pipe I took my time and was very careful and have no doubt those items are in good shape and installed correctly. Other than the silt my water is crystal clear and I have no other issues.

Thanks
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
Any silt coming from the sand filter should be flushed out and collected by your robot.

I have the same environment as you and the robot cleans it just fine. If you have it occurring often, do take a look at your chemistry.
 

Tfastle

Active member
Mar 17, 2014
43
Albq. NM, United States
I am not sure what you mean by "flushed out". You mean when I backwash the filter or flushed out of the filter into the pool? I assume you mean when backwashed. After I have backwashed I still have the same issue. I believe the silt is going through the filter and thus, not collected and not able to be backwashed out. But maybhe that is not what you mean.

As I mentioned above, the silt comes from the filter and is most noticeable where the returns go into the pool. One is over a tanning deck and it will be clean. If I close the pool and run the pump there is always silt settled on the tanning deck (water is about 6" deep there). I brush off the steps and deck, run the cleaner and for the most part it's good. If I leave the pump off then it stays fairly silt free. As soon as I run the pump for any period time silt begins settling out.

How might my chemicals cause or impact this problem? I mean cause silt in the pool?

Thanks
 

Tfastle

Active member
Mar 17, 2014
43
Albq. NM, United States
It's too fine to rub between your fingers, or to catch to rub between your fingers. If you rub a puddle or collected spot of it with finger against the bottom it is like a very very very fine grit. It basically dissipates when you brush it, into a light cloud that, as it spreads it almost goes away but you can watch as some if it starts to settle again. If I brush the entire pool it looks clean but in 20-30 minutes it begins to settle again and you can clearly see it. In some areas it's uniformly spread so it just looks a little off color and in some areas it "puddles" and looks like debris or such until you brush it and it's clear that it's silt by how it goes into a cloud. The color is light to medium brown. I just went out and took the basket out of my robotic cleaner. Quite a bit collects there and it's like mud that is so fine that it is almost not gritty at all. Where we live it's at a mile high, dry desert type environment. Lots of dust. By that I mean, if you don't ride your bike in a couple of days, there is a thin coat of dust on it when you go back to it. This stuff looks like silt that this dust would create. It's not pollen, which I would get in my other pool in another part of the country which acted quite similar as far as clouding but my filter even filtered that out.

In that pool in my prior home I would have similar silt at times but I would run my filters, brush it to mix it with the water and it would go away. I assume it was captured by the DE filter. The more I ran that pool the cleaner the water was. This pool I have to balance between keeping my chemicals up and filtering and not over running it because, the longer I run it the more silt ends up in the pool. The only way I can get it to minimize is if I turn off the pump and run my robotic with a silt basket in it and not run the filter afterwards although some still settles out. I'm fairly sure the robotic cleaner can't get it all and so, the silt still in the water ends up settling.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
Do you wait until your filter pressure is at least 25% higher than clean pressure prior to backwashing? A dirty sand filter filters better.

As you are fully convinced it is a filter issue, your best bet is to investigate getting a DE or DE Hybrid filter. That will provide the best filtering of very fine solids.
 

Tfastle

Active member
Mar 17, 2014
43
Albq. NM, United States
Clean pressure is around 14psi, I generally backwash around 28-30psi which is what I was told when the pool was new, to backwash when it goes up 15psi.
I'm not fully convinced it is a filter issue but common sense sort of dictates that as far as I can tell. I could be wrong but have not heard any other possibilities. I'd rather not have to go to the hassle and cost of replacing the filter which is why I asked my original question - Is there a way to get a sand filter to filter finer particulates? (the ones I have heard about but am a little dubious of are adding a little DE to the sand and then alternative media like glass beeds)
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
The only method we endorse is adding DE. Alternative media is very hit or miss. TFP believes sand filters should use sand.

You are waiting way too long to back wash. I imagine your water flow is way down or you have a variable flow pump that ramps up its rpm to keep your flow as the pressure rises.
 

CUTiger78

Well-known member
May 24, 2009
466
NoVA
Give the addition of DE a try. I did that w/ sand in my filter & now w/ Zeosand in my filter. Get a bag of the synthetic DE, it's cheap. I believe the occasional addition of DE has improved my fine filtering when I needed it. Certainly didn't hurt anything.

BTW, I've been using Zeosand for a few years. I think I'm happier w/ Zeosand, but I don't have any hard data to use for comparison.

Cheers!
 

rowiac

Well-known member
Apr 20, 2018
73
Tehama County, CA
I'm using Fiber Clear cellulose filter media instead of DE in my sand filter. It's biodegradable and non-carcinogenic (or so they say). You add enough for your filter pressure to go up by about 1psi from freshly backwashed. I've been using it since I SLAM'd, so I don't know if it's what keeping the pool clear, but it hasn't hurt anything either.