DE in Sand Filter...how often to backwash?

[jstkiddn]

I added some DE to my sand filter yesterday as outlined in the sticky at the top of this forum. (btw - the difference in my water overnight is AMAZING! )

When I picked up the DE at our local pool supply store, the older gentleman that runs the place told me that if I used the DE in the sand filter I need to backwash every two days or "the DE will work its way down into the sand".

Is this so? Do I need to follow some specific backwashing schedule if I'm going to use the DE?

[PoolDoc]

"DE will work its way into the sand" And that's supposed to be a problem? Good grief.

On a sand filter, you need to backwash when the pressure increases (and the flow drops). Often, an increase of 4 - 7 pounds is cite; just looked at a couple of PacFab (Pentair) manuals and saw a 10# increase noted.

I hadn't read those manuals in years, and was surprised to see that they all say the BEST way is to use a flowmeter, and backwash when flow drops 30%. If you want to do that, here are some flow meters that work pretty easily. Be sure to install them AFTER the filter, since dirt will plug them up.
http://www.poolpartsonline.com/p-333-flow-meters-blue-white-top-mount-f-300-series.aspx
or
http://www.a1poolparts.com/-strse-1048/BlueWhite-Flowmeter-for-3/Detail.bok