Need some clarification on using DE with a sand filter

[Brentr]

Hello, my friend brought this to my attention. I have seen posted that you can add DE to a sand filter and you would get better filtration. How is that possible????? Sand filters filters up to 10 microns so if you added DE which filters up to 2 microns then it should pass thru the sand. Is that correct? Can someone please explain in detail what is happening when you add DE to a sand filter?
Thanks in advance

 

[woodyp]

10 and 2 microns are NOT the sizes of the sand or the DE. DE just helps catch the smaller stuff.

 

[Richard320]

Think of sand as a screen with 10 micron holes and DE as a screen with 2 micron holes. The DE sits on top of the sand. Nothing bigger than 2 microns is going to get through.

 

[Brentr]

If sand catches particles bigger than 10 microns then anything smaller will filter thru it. DE particles is smaller than 10 microns so it would filter thru the sand. Does that make sense??

 

[Richard320]

If sand catches particles bigger than 10 microns then anything smaller will filter thru it. DE particles is smaller than 10 microns so it would filter thru the sand. Does that make sense??

No, DE particles are a lot bigger than 10 microns. You can see each individual speck of it with the naked eye, like flour. DE is not a tiny rock like sand. DE looks like a sponge under a microscope. The water goes through the particles, not through the gaps between them.

 

[Brentr]

Richard320, Diatomaceous earth (pron.: /ˌdaɪ.ətəˌmeɪʃəs ˈɜrθ/) also known as D.E., diatomite, or kieselgur/kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that is easily crumbled into a fine white to off-white powder. It has a particle size ranging from less than 3 micrometre to more than 1 millimeter. So if this true will the smaller particles less than 10 microns flow thru the sand filter? This seems to make sense to me. I welcome all opinions. Thanks in advance

 

[toofast]

So as a follow up to this...based on this concept doesn't the DE catch ALL the dirt and the sand simply does NOTHING ? Assume we would have to backwash a TON more using DE on top of SAND ?

 

[JasonLion]

Nothing catches all of the dirt, some stuff always gets through.

When you add DE to a sand filter, you do need to backwash a little more often, but only a little.

Adding DE to a sand filter is much better than sand alone, but not as good as a true DE filter. The DE does not form a solid layer across the entire sand bed, if it did the filter would stop working. DE filters have far more surface area than sand filters. The added DE catches only a small percentage of the finer particles on each pass through the filter, but over time as the water passes through the filter many times it will eventually get almost everything.

 

[toofast]

Ah, ok...makes total sense.