sand filter sand question

[avemaria]

I'm actually setting up a sand filter for the first time and am confused about the various sand.. I was about ready to buy the Zeobrite for its lighter weight and filtering ability but then i went to another forum and read the posts about it.. so i decided being i'm not even familiar with how this filter is going to work i might as well just stick with what they recommend.. which is #20 silica sand or particle size range of 0.45 to 0.85mm. I checked Pinch A Penny and the only silica sand they seem to have is something with a 20/30 label.. 30 is still in the range above but i'm wondering if anyone else uses 20/30 in the Intex 2650gpm filter...

I'm not going to post the link but here is what they say about the sand

Florida Silica Sand 50 Lb. 20/30 Grade Filter Sandhttp://www.poolforum.com/pf2/modcp/moderate.php?do=posts#

Pool filter sand is a quality filter media that has been washed and specifically graded for use in sand pool filter systems. This 20/30 grade pool filter sand is the best grade for filtering pool water, according to sand pool filter manufacturers. Follow your filter manufacturer's instructions for proper application and backwashing.

I'm just lost right now and am wondering if I should get this or seek out plain standard #20 silica sand.. I think Ace carries it online..

[PoolDoc]

I can't answer your question (which should I get?) directly, but I think I can provide some info.

I've experimented with different grades of sand, and I can tell you that all of the following are true:

1. Sand that is too fine causes problems, by getting caught in the grids in the laterals, by washing out during backwash, and by damaging valves down stream of the filter (filter side, and backwash side) by getting into stems.

This is the reason you MUST not use masonry sand. I have personally replaced over $2,000 worth of 8" commercial butterfly valves destroyed by masonry sand.

2. Coarse sand results in poor filtration. One of the large local pool stores in my own area decided to make more money by buying 100# bags of sandblast sand and selling them for filter sand. The sand blast sand was actually more evenly graded than most of the filter sands I've seen, but it was also a bit coarser. Over the years, I removed it from a half-dozen large commercial filters, and replaced it with proper filter sand. Every pool experienced a substantial improvement in water quality as a result.

3. Not all filter sand is created equal. "No. 20 standard silica (uniformity coefficient not greater than 1.75) .018-.020 in diameter particle size" (as specified by Pentair) doesn't necessarily compare well to what's sold: "QUIKRETE® Filter Sand has a predominant size range as follows: US Sieve Size 20-40 - Particle size (0.85-0.425 mm)" (0.85 - 0.425mm => 0.33 - 0.167 inches!) As you can see, the Quikrete sand is much coarser than what Pentair specifies!

3. Fine sand produces better results. A number of years ago, I bought several hundred pounds of a fine grade of sand blast sand, that was finer than filter sand, but much more uniform than masonry sand. I placed a 4" layer of this sand in each of a battery of TR160 (36") filters, and then covered it with an 8" layer of regular filter sand. Water quality went from clear (30' under water visbility) to very, very clear (80' underwater visibility. But I did have some damage to the multiport valves over time.

Just reading over this -- it's probably less useful to you than I would have hoped, but it's what I've got. Sorry!

ref: http://www.lancasterpump.com/documents/filtersand.pdf
http://en.wikipedia.org/wiki/Mesh_%28scale%29
http://www.pentairpool.com/pdfs/TritonIIOM.pdf