DE coming through sand filter, is this normal/possible ?

[spica]

I have decided to try to add some DE to my sand filter. I have followed the recommendations in another thread by premixing a little bit of DE at a time and waiting approx. 20 minutes for a pressure increase. I've added about 1/4 cup each time, but no pressure increase. I've noticed though that the water became cloudy. I then did a little experiment by adding another 1/4 cup and I can see actually see the return becoming cloudy right after adding the DE, i.e. the DE (or perhaps most of it) goes right through. My filter and sand is only 3 weeks old. The sand is the correct type and amount (aquaquartz 0.45-0.55mm, 100lbs). I run my filter mostly at 15GPM and sometimes at 27GPM, the S166T has a "design flow rate" of 35GPM, so I don't suspect any channeling could have developed. From what I've read, sand filters should filter around 20-100um particles and according to wikipedia, DE is typically 10-200um, so a sand filter should filter most of the particles. Am I missing something here ? Any help would be greatly appreciated.

Thanks,
N.

14' 1500gal intex AG
hayward S166T filter
hayward max-flow 1.16HP 15/27GPM
120sq ft solar panels

[PoolDoc]

Am I missing something here ?

What you are missing is the fact that the 'design flow' is bogus. It's not your fault that you don't know that: the pool industry doesn't advertise the fact. But, there it is.

I don't know how they came up with that figure -- 25gpm/sft filter surface -- but it's unrealistic.

Years ago when they began replacing "slow rate" sand filters with 'depth filtration' "high rate" sand filters using "depth filtration", they were pushing the envelope with 15gpm/sft on a sand bed (in the Baker Hydro HRV) that was easily 18" thick. It worked -- not as well as the slow sand filters (5 gpm/sft) -- but it worked. Dirt retention in a sand filter is a function of sand particle size, flow rate per sft, and filter bed depth.

My experience, with many large (>100,000 gallon) commercial pools has been that filtration at 12gpm / sft is noticeably better than at 15 gpm. And it also improves if I 'overload' the filter with sand, increasing the thickness of the bed. When I installed my last set of commercial filters, in 2010, I used (3) 60" filters, loaded to a 30" sand bed depth, filled with gravel, then filter sand, then extra fine sand, then filter sand, and limited to 12-13 gpm / sft. With those filters, I routinely get 120' underwater visibility, in a heavily used commercial pool.

Your filter has about a 10" sand bed depth (1/3 of my big filters), running at 25+ gpm/sft, when you'd have to run at about 7 - 8 gpm to filter like my filters do.

That pump and filter package left the factory in as a sub-optimal design, 'broken from the factory'. To 'fix' the problem, you need to do two things:
1. Open the filter and replace any missing sand. Odds are, you've been losing sand on each backwash.
2. Install a valve or other means that allows you to throttle flow to about 15 GPM (PLENTY for a 1500 gallon pool)

Then retest with DE -- but use 1 cup at a time.

[spica]

Thanks Doc.

I did the following:
1. Verified sand level. Open up filter, it's at approx. 11" where it should be.
2. Back-washed filter up any channels if they existed.
3. Ran 2 cups of DE through one cup at a time, at 20min. intervals. No increase on filter pressure gauge, stuff goes right through (cloudy return)
4. Verified flow rate with bucket test. 18GPM i.e. 12.8GPM/sqft with solar panels off, 12GPM with solar panels on
5. Ran filter through the night at 18GPM

Thanks for the valuable information on the flow rate. This is not a factory pump-filter combination. I already had the pump and bought the filter on the basis of the "design flow rate". I feel like I have been robbed in broad daylight. If they didn't have bogus flow rates, I wouldn't have minded paying just a little extra for a larger filter.

This morning the pool was clear, the DE just settled to the bottom. I'm sure it's DE because of the color and texture. I ran another 1/4 cup through this morning, and same thing, goes right through, cloudy return.

I then vacuumed the DE from the bottom surface. It's difficult to see, but it looks like it still goes right through the filter.

I have to admit that the DE is not from a pool store. It's a brewery grade, the datasheet states that 96% of the particles are smaller than 105um. A sand filter should therefore catch the larger particles and progressively catch the smaller particles as the DE also starts working as a filter medium.

Questions:
1. Does anyone have experience with the sand I have in my filter ? (Aquaquartz brand)
2. Does the DE trick really work ? I have a very small pool and I can see when a cup of something clouds up the pool. On larger pools a cup might will dilute and not be recognisable.
3. It would seem my filter is not working like it should. Is there a simple test I can perform to see if it performs like it should ?

Any recommendations are welcome.

Thanks,
Neels.

[PoolDoc]

I then vacuumed the DE from the bottom surface. It's difficult to see, but it looks like it still goes right through the filter.
I have to admit that the DE is not from a pool store. It's a brewery grade, the datasheet states that 96% of the particles are smaller than 105um.

I've always suspected that this would happen -- but we haven't had confirmed cases of people using non-pool DE. Now, we have. Until you test with pool DE, your test tells us nothing.

Does the test really work? Depends on what you mean. If you mean, does using pool DE to check filter function work, the answer is "Yes, generally". If you mean, does it work to use DE to enhance sand filtration, no, not really (sorry mods!). A tiny sand filter coated with DE is converted into a microscopic DE filter.

Here's what I mean: a minimally sized sand filter, for a 25 GPM flow is going to be 18" in diameter. Except for the shallow sand bed, your filter (at 16") is OK at 18 GPM. But, a minimally sized DE filter for 18 GPM is going to to have 9 sft of surface . . . and yours has only 1.36 sft. So you take a marginally acceptable sand filter, and turn it into a DE filter that is 1/6 of a marginally acceptable size.

[spica]

Yesterday, I bought a bag of pool DE (EP Celatom SP) and poured 2 cups of it into the system. My filter pressure guage increased almost immediately. Nothing was visible through the return.

I left the filter running overnight, and this morning the water is crystal clear. Now I'm also able to filter the non-pool DE that has settled on the bottom, and now the return water is clear. I was a little concerned as to how to get rid of it.

Interestingly enough, both the pool DE and non-pool DE (EP Celabrew CB6) are very similar (both flux-calcined) except that the pool DE has 80% of particles below 105um as oppose to 96% of the non-pool DE (according to the datasheets). Perhaps the larger particles helps the coating process to develop faster. This might explain why other members have had experiences where there DE took a while before they saw a pressure increase. Perhaps their DE contained mostly smaller particles (since they vary from lot to lot) and it took a while for the DE to coat. When doing this an automatic cleaner would be essential to bring back the DE that has settled to the floor.

The DE definitaley enhances sand filtration, since I can now pick up material I never could, but it won't replace an equivalent DE filter. I don't think I'm going to use the DE in my filter anymore, water is fine as it is, but it might be handy when cleaning up really fine stuff (dead algae?). Now I have enough DE to last for the next century.

We'll now we know non-pool DE is probably not a good idea. Thanks again Doc.
N

[Watermom]

Thanks for reporting. Also, thanks for the subscription!

[PoolDoc]

Thanks for sharing your experiences - the info will help others.

[kelemvor]

Now I have enough DE to last for the next century.

You can also use it for pest control (especially slugs!) in your garden or for cleaning up oil in your driveway if you've got a teenager who changes his own oil.