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Location: Wake Forest, NC USA (in Central NC, God's country)
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Problem with Sand-Based Pool Filter

09/10/2009 3:52 AM

I recently rebedded the sand filter for our above ground pool thinking that age (about 7 yeears) was the reason that fine particulate matter was not being removed from the water. However, the water still remains cloudy and when sediment is vacuumed from the bottom after the pump has been idle for a couple of days, most of it appears to pass right through the filter medium. Is there a problem here, or is sand just not very efficient as a filter medium? I hate to lose water by always vacuuming sediment to waste. Chlorine levels are kept adequate and the pH is maintained at about 7.6. I use both calcium hypochlorite and triazine-based chlorine at various times. Thanks for your help.

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#1

Re: Problem with Sand-Based Pool Filter

09/10/2009 4:52 AM

Had the same problem, the rubber seal in the valve housing on top of the filter gets worn, and the water passes across the seal, not passing through the sand, which has greater resistance?

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Commentator

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#10
In reply to #1

Re: Problem with Sand-Based Pool Filter

09/11/2009 6:08 AM

The whole valve was just replaced a couple of months ago because of leakage to the waste port with loss of water.

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Active Contributor

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#2

Re: Problem with Sand-Based Pool Filter

09/10/2009 4:52 AM

Hi,

Did you thoroughly rinse the sand before replacing?

I think that 4 years is about the life span of filter sand.

There are additiives which one can add which bind the fine sediment and stop it from being released into the pool, speak to your pool guy.

If this is not an option remove all automatic pool cleaners and allow the pool to filter for a day or two. The sediment should collect at the bottom. Take a manual vacuum and vacuum out the sediment with the pool pump selector set to waste. This will take the sediment directly out of the pool and not through the filter. There is a tendency to try go to quickly in order not to waste too much water. Don't fall into this trap, all you will do is to stir up the sediment. Make sure your pool is full before starting, you would not want to drop below the wier halfway through.

Andrew

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#13
In reply to #2

Re: Problem with Sand-Based Pool Filter

09/11/2009 7:25 AM

They don't change the sand at the beach for good reason, it lasts a lifetime.

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Join Date: Oct 2008
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#16
In reply to #13

Re: Problem with Sand-Based Pool Filter

09/11/2009 9:37 AM

The beach replenishes its self as the grains of sand get broken down and you no longer see the silt.

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#3

Re: Problem with Sand-Based Pool Filter

09/10/2009 8:53 AM

Use a product such as omni-clear. It binds the fine particles into larger clumps to filter out. Follow directions on bottle as using too much acts as a dispersant.

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Commentator

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#4

Re: Problem with Sand-Based Pool Filter

09/11/2009 2:12 AM

Yes I believe these are called anti-floccukants such as Joli Jellie and pool clear,both will bind the fine particles and get rid of the cloudy stuff.Good Luck.

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#23
In reply to #4

Re: Problem with Sand-Based Pool Filter

09/11/2009 12:11 PM

actually those would be flocculants, not anti-flocculants, and the large sturctures formed are flocs.

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Guru

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#5

Re: Problem with Sand-Based Pool Filter

09/11/2009 2:36 AM

Take one or two layers of polyester velvet fabric used for automobile seat covers, pass turbid water from the raised velvette top face and check the clarity of filtered water.

If you find the effective performance, improvise a velvette cloth filter suitability to your end use including back wash provisions. A simplest , viable low cost long time workable water turbidity removal filter.

Try and report feed back.

Regards

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Commentator

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#11
In reply to #5

Re: Problem with Sand-Based Pool Filter

09/11/2009 6:12 AM

I'll try this when I can get some of the fabric. Thanks. This sounds like a good solution if I am able to rig up such a cloth filter.

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Guru

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#27
In reply to #11

Re: Problem with Sand-Based Pool Filter

09/13/2009 10:44 AM

These fabrics are available plenty in furnishing, upholstery or floor mat whole sale shops. Enquire and search. I am sure you can get it without much difficulty. Best wishes.

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#6

Re: Problem with Sand-Based Pool Filter

09/11/2009 4:14 AM

Perhaps you should actually replace the sand. Make sure you use sand that is specified for use in pool filters and not just any sand.

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Commentator

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#8
In reply to #6

Re: Problem with Sand-Based Pool Filter

09/11/2009 6:01 AM

The sand had just been replaced with sand specified for use with pool filters.

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Guru

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#7

Re: Problem with Sand-Based Pool Filter

09/11/2009 5:50 AM

Got a Pollen problem it sounds like and a Paper Filter is needed

pollen is carried by the wind your fighting a losing battle without a paper or fiber filter to hold the pollen for removal .

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#9
In reply to #7

Re: Problem with Sand-Based Pool Filter

09/11/2009 6:06 AM

I'm pretty sure this stuff is not pollen. The months of heavy pollen in this area (east central NC) are April and May.

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#12
In reply to #9

Re: Problem with Sand-Based Pool Filter

09/11/2009 7:00 AM

My hot tub is near some tree and even now in Tennessse pollen falls off the leaves. Yellow globs in the bottom of the hot tub if I don't run it daily.

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Guru

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#14

Re: Problem with Sand-Based Pool Filter

09/11/2009 9:06 AM

Greetings ~

#4 was 'close'... a "flocculant" might help...

By the same token, the quality of your (initial-fill & 'make-up') water, pool finish, bather load (everyone's chemistry differs slightly), and multitudes of other factors just MIGHT make *your* pool a candidate for a DE (diatomaceous earth) filter.

I learned many things during a stint as a state certified pool and spa contractor (in Florida) some years ago (hate to think how many)... the most important being:

each pool has it's own "personality", based on the above-named factors, and, there is NO "cut-and-dried" answer to anyone's problem, based on an incomplete analysis.

DE filters work better than paper cartridge or sand filters ... measurably and noticibly better in most instances. But three caveats apply:

1) Sizing the filter properly is imperative.

2) Sufficient filtering time each day is imperative.

3) Maintaining the filter properly is imperative.

Horsepower keeps your water clear...NOT chemicals.

Best wishes to you---

"PS"~~ this post is NOT intended to answer all your pool water chemistry needs. It addresses ONLY the crux of the OP...

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Commentator

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#20
In reply to #14

Re: Problem with Sand-Based Pool Filter

09/11/2009 10:02 AM

Thanks. I was actually considering adding some diatomaceous earth to the sand filter through the strainer to improve filtration efficiency, but this process might wind up ruining the sand filter according to some internet sources.

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#15

Re: Problem with Sand-Based Pool Filter

09/11/2009 9:24 AM

I had the same problem 2 years ago with a minor re-occurrence this spring. The solution to my problem turned out to be caused by my adding Na2CO3 (pH-UP, increases pH) too fast resulting in localized precipitation of chemicals already in the pool, probably copper and other metals. Once formed you can not re-dissolve them without decreasing the pH to much lower than your equipment can tolerate so you will have to physically remove them.

The precipitate is too finely divided for the sand to trap. Flocculantes make small particles "clump" together to form larger particles that can be easily removed. The problem with flocculantes made for pools is that they are designed specifically to bind dirt, pollen and other common pool particles together. They do not have the correct charge or molecular weight to be effective with this precipitate.

Three weeks of treating the problem per my local pool dealer "expert" advice did not improve anything but their bank account.

I aimed the filter discharge as far to the side and 30° down so that it made the water swirl. The next day I turning the pump off for 3-4 days so that all of this material settled in the center of the pool. I then set the filter to waste and vacuumed the material up and out. I only lost ~50 gallons.

The reason that periodic replacement of sand is recommended is over time the sharp edges and points of the sand grains wear down making them smaller. This allows the sand particles to pack closer together making a more dense filter media. This improves filtration efficiency at the cost increased resistance to flow. This causes the pump to have to work harder to move the water through the filter and consequentially consuming more power and reducing the life span of the motor and the pump. To visualize this, think of water flowing through gravel vs. sand vs. clay. Water passes freely through the gravel, is slower through sand and may not pass through the clay. The flow rate is directly related to the void space between the particles, finer particles, less flow.

Good luck with your problem.

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Commentator

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#18
In reply to #15

Re: Problem with Sand-Based Pool Filter

09/11/2009 9:54 AM

Thanks. Sounds like a nice simple fix! Will try it.

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#25
In reply to #15

Re: Problem with Sand-Based Pool Filter

09/11/2009 12:19 PM

Actually flow rate is not directly related to void space, as clay has a fairly high void space. Flow rate is related to porosity, which is the continuous macropores that make up a portion of the void space, in finer particled materials many of the pores are not continuous.

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#26
In reply to #25

Re: Problem with Sand-Based Pool Filter

09/11/2009 6:36 PM

You are correct, I mis-typed. Thank you for catching my error. Lord knows somebody needs to keep an eye on me.

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#28
In reply to #26

Re: Problem with Sand-Based Pool Filter

09/14/2009 11:28 AM

Well, I am not clear also, I should have stated that it is related but not directly related to porosity. It is related to the continuous pore space, but there is discontinuous pore space, which increases as the materials get finer grained. Also, there are the size of the pores that plays a major factor on the rate at which water flows, as many smaller pores of same cross-sectional area will not conduct water as fast as few large pores due to surface friction with the pore walls. There are, however, numerous equated relationships for a variety of soil materials over a variety of limited gradations ranges that relate porosity to conductivity of the material. Of course these are experimentally based, and many occupy same gradation ranges and will provide significantly different results usually within 1 or 2 order of magnitude of each other.

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#17

Re: Problem with Sand-Based Pool Filter

09/11/2009 9:43 AM

Were you careful when dumping the rock and sand in and not cracking or breaking a finger off? Also give it a good backwash as you could have channeling.

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#21
In reply to #17

Re: Problem with Sand-Based Pool Filter

09/11/2009 10:19 AM

Yes, I was very careful about that.

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#19

Re: Problem with Sand-Based Pool Filter

09/11/2009 10:01 AM

Do you only check the chlorine and pH levels? My water was cloudy earlier this year. My alkalinity was low. I believe I eventually added 15-20 lbs of sodium bicarbonate to get the alkalinity to a good level. The pool has remained clear since then.

I have also had problems with the filter causing the pool to be cloudy. I replaced my filter 3 years ago (my old filter was 20 years old). My pump started working better and my water was clearer. I generally replace the sand every couple years (above ground pool) because it gets clogged with dead skin cells, oil, ... The sand doesn't cost that much and it's not worth the hassle and cost of using chemical cleaners, etc. to improve the efficiency.

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#24
In reply to #19

Re: Problem with Sand-Based Pool Filter

09/11/2009 12:13 PM

Because of the acidic nature of the rainfall here, I use a lot of bicarbonate and carbonate to maintain a pH above 7.5 and so alkalinity is not likely to be an issue.

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#22

Re: Problem with Sand-Based Pool Filter

09/11/2009 11:38 AM

Add in a sediment filter on the high pressure side for a few days! and 1/4 cup muractic acid

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#29

Re: Problem with Sand-Based Pool Filter

09/22/2009 7:49 AM

Seems to be a problem with clay or other fine particles

Alum is a good flocculant and is cheap.

Epsom salts can also be used but has quite an effect on anyone who happens to drink the water while swimming!

When travelling out back, many people carry a small amount of alum to clarify water from clay lined dams.

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#30
In reply to #29

Re: Problem with Sand-Based Pool Filter

09/22/2009 8:02 AM

Thanks, Sceptic..

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#31
In reply to #29

Re: Problem with Sand-Based Pool Filter

10/12/2009 3:37 AM

I agree with your assessment that the problem is fine particles. As for Alum (aluminum sulfate) or Epsom salt (magnesium sulfate) being good flocculants and cheap as well, I also agree. Ferri-Flocc (ferrous sulfate / ferrous aluminum sulfate) and gypsum (calcium sulfate dihydrate) are to other ones.

However, as I posted earlier, any flocculant is only effective when it has the correct charge, is the correct type; i.e. anionic, cationic or non-ionic and in many cases has the correct molecular weight.

Normal pool flocculants and clarifiers did not work for me on my pool problem and I do not believe they will be effective in this case (based on my experience at home and at work).

The ones you mention will affect the pH of the pool and could cause other problems including forming additional particulates in the pool. Pool flocculants and clarifiers are specifically selected or created so as to not cause additional problems. They work best on dirt, dust, pollen and other airborne pollutants that get into pools. In my case (and I believe this one) my problem was not any of these.

Some general information can be found at: http://www.flocculants.info/ , also at the websites of GE Betz, Allied Colloids, Ciba, Cytec and others.

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