Can I add some DE to a sand filter

[PoolDoc]

It's not clear to me why you want to add DE to your filter. It's useful if you suspect your sand filter has problems or needs more sand. But it's rather less useful if you are hoping to enhance filtration: if there's anything in the pool water that your sand filter is not stopping, you'll need to be ready to 'babysit' the filter once you add the DE. Pressure can rise very rapidly.

It *is* true that, in a sand filter, the dirt become part of the filter media, as the filter gradually collects smaller and smaller debris. This is where the 10# rise comes from. But there's a trade-off. As the pressure increases, flow rates drop. So, you end up filtering less and less water.

As far as when you backwash after adding DE, there is no 'magic' number, but it would be reasonable to backwash on the same pressure increase as you do normally.

[schutt982]

I wanted to add DE to "enhance" my filtration. I seem to have a problem filtering all the pollen (green powder) and dead algae (white powder) during spring startup. My water was cloudy. I popped the top on my sand filter this past weekend and the sand seems good - fine and smooth, no channeling, no gunk or clumps. It was about 2 inches lower than the fill level for when the tanks starts curving in. I figured that was fine.

I added 1 1/2 cups of DE to my sand filter. PSI went up 1 PSI as expected. I immediately watched the outlets to see if any of the DE "white powder" came flying out. Previously, I could always see the water coming out from my outlets jets. I could see barley discernible underwater stream of water that I always thought showed small air bubbles or the turbidity of the slightly cloudy water. One minute after I added the DE the water was so clear that I could no longer tell that water was coming out of my jets! (except for where it rippled the surface of the water). I vacuumed my pool, PSI went up 5 more PSI, I backwashed and then added the same amount of DE again. Pump PSI stays stable at +1 PSI over normal and the water is crystal clear - it looks "polished"!

I think I will continue to use DE in my sand filter.
I plan next to add salt and borax to my BBB pool for those enhancement effects.

[Watermom]

Good deal. Glad it helped!