Can I add some DE to a sand filter

Love these forums! Have not really been happy with the pool store advise and prices and when they messed me up once again I started seeking solutions on my own. I will be starting a BBB routine.

I am thinking of adding some DE to my sand filter (14 yrs old). Advise from forums is to only add enough (1/2 cup in a slurry at a time - up to 1 to 2 cups, added to skimmer) to raise the gauge pressure by 1 PSI. There is a caution that pressure may increase significantly over a short period of time or that the DE may come back out through the returns. My current pressure is only around 8 psi since I've dumped allot of water to lower the CYA (was 65) to begin a SLAM process for cloudy/foamy water. I will wait until the pool is balanced before adding and DE.

I have lots of questions but my ONE for now is:
1) When I do add some DE what PSI is a significant rise in PSI that would prompt me to backwash?


I normally wait until a 10+ psi increase before I backwash. I assume the a rise in PSI is simply the filter media (sand only or sand/ DE) is getting clogged? I have also been told that if you backwash too often your filtering media will be to "clean" to effectively filter small particles from your water. I had to backwash often last year due to excessive rainfall and felt that my filter media was not catching the small stuff.

16 X 32 in-ground vinyl pool, Hayward sand filter and pump

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.

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.

Good deal. Glad it helped!