My findings on how not all sand is created equal

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nealyak said:
Though just looking at the larger grains in the pictures posted here. A lot of those grains are much bigger than 1 mm. So I don't think the HTH sand has a #20 upper limit well enforced.
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The HTH sand looks a little big, whereas the Quikcrete sand looks a little small.

It would be interesting to know the gap size in the laterals so that we could know what the minimum size sand grain should be.

Knowing the lateral hole size and the sieve analysis should help identify which sand would be a better choice. A sand with virtually no grains below the lateral hole size would be best.

Maybe someone could ask a manufacturer or measure the gap size themselves?

One could also ask what would be the ideal sieve analysis for filter sand? The smallest particles that won't go through the laterals so that they pack tighter and filter better? A mix of sizes? Maybe a layering of sizes?

Perhaps a layer of larger grains at the bottom with a layer of smaller grains on the top? (This might work for a while, but might eventually fail if the smaller grains work their way to the bottom due to something called the Brazil nut effect).
 
Here's a sieve analysis from a manufacturer of pool filter sand.

Sand and Gravel Water Filtration Media - Red Flint

It indicates that about 2 percent will be less 0.425 mm. So, about 2 pounds per hundred pounds of sand. But, only a small amount of it would be near the laterals.

If someone wanted to determine whether the sand in question was within specifications, they could buy a #40 sieve and see what percent of the sand passed through. It's probably not worth pursuing unless someone really wanted to make a point.

To check the hole size in the laterals, a spark plug feeler gauge would probably work well. They're inexpensive and readily available. I would think that the minimum sand grain size should be somewhat larger than the slits in the laterals. Perhaps 50 % larger. I would also think that at least 99 % of the grains should be larger than the minimum.

For example, the above referenced sieve analysis indicates that 99% is greater than 0.355mm. Using the formula proposed, the maximum lateral slit size would be about 0.24mm.
 
I checked two different sets of laterals using a mechanic's feeler gauge set. The best fit was 0.33mm. However, gauges up to about 0.4 mm would go through with some pressure. I would think that a 40 mesh (0.425mm) would be a good lower limit.

Technically, if a sand lists an effective size of 0.45 to 0.55 mm, it could have up to 10% by weight that is smaller. So, it depends on the manufacturer's quality control. They might consider 10% smaller to be acceptable.

In my opinion, I think that I would want less than 1% to pass a #40 sieve and more than 99% to pass a #20 sieve. I think that a uniformity coefficient of between 1.0 and 1.75 would be a good choice.
 
I will email my friend who is a production engineer with Pentair filters. He should be able to shed some light.
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From a pentair filtration engineer...

The sieve size data that is being described in the thread is correct. Any #20 silica sand is our recommendation. From the pictures, it does look like the HTH sand is a bit coarse and the quikrete looks a bit on the small side, although probably ok. Its impossible to really tell without actually running it through a sieve.

We typically use US Silica Mystic White II sand here for all of our testing. It may not be readily available at Ace/Home Depot though. In general, I’d recommend getting your pool sand from a pool supply store and not a hardware store as they are far more likely to stand behind what they sell than a big box store but I can appreciate how a lot of forum members are trying to save a buck or two by having more in depth knowledge.
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My takeaway from that is it really does make sense to buy from a pool store....the Big Box stores simply do not care.
 
The Mystic White® II brand Pool Filter Sand looks like it would be a good choice.
http://www.texasaquaticsupply.com/docs/Filtration%20Equipment%20&%20Supplies/Mystic%20White%20II%20Filter%20Media/U.S.%20Silica%20Company%20-%20Mystic%20White%20II%20Pool%20Filtration%20Media.pdf

It has various effective sizes. Listed are
"Effective Size - .49 mm, .65 mm or .80 mm. (Other sizes available on request)"
It seems that some laterals might have slightly larger openings than others. For Intex, a larger sand might work better. If one wanted to get better filtration without having sand wash through the laterals, they might start with a larger effective size and then switch to a smaller effective size near the top.
 
Just reporting back. My laterals measured about .45 mm (Hayward S244T old screw in style laterals). But I could force a .55 mm feeler through without much effort. Additionally, when I pulled my laterals out there were many sand grains already wedged firmly in the lateral slits. This cannot be good and probably restricts flow.

Also, I never heard back from HTH and the Hayward's rep. simply parroted back what the manual says and ignored questions about lateral size.
One question the Haywards rep did answer was layering different types of sand would not work due to mixing of sand when backwashing.

How much does the Mystic White II sand cost? I cannot find it anywhere. I am wondering if its almost better/cheaper to go with the Zeo Sand at this point. Does ZeoSand last for the life of the filter?
 
I bought the quikrete at home depot. Was told to do major backwash before trying to filter the water. Did That and noticed a real slurrey coming out. After two backwashes the sand filter tank burst. Yes the tank was quite old, but thought interesting when I took the sand out, it was very much heavier than what I had used before. Used to be able to use wet vac, but this sand I had to shovel out.
Now the reason for the post, looking sand filters, had a Tagleus 60. Pentair makes a similar model under their own name which is half the cost of the Tagleus which is made by Pentair. Why would one cost twice the other one. Reviews of the Pentair had several burst at the seam after a year or two. Might it be much thinner fiberglass?
Definitely will buy the HTH sand next time.
 

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