So I got some DE to add to my sand filter as it was taking a long time to clear the water. Oddly enough I pulled the cover off and despite the bottom have a nice layer of gunk the water was very clear. I decided to add the DE anyway.
Followed the instructions I noted the pressure, barely below 15 PSI, and started adding DE by 1/4 cups. The instructions say 1 to 2 cups usually raises it the required 1 PSI. I stopped at 2 cups and the needle had barely moved, I'd say not much more then 1/3 PSI.
I decided to go ahead and vacuum the gunk and I guess the DE was doing it's job because as I vacuumed the pressure went up. It went up considerably enough that I decided to Backwash. After back washing the pressure dropped down even further the the original 15 PSI.
So two questions.
1. Do I continue to add more DE even over two cups until the pressure goes up one PSI?
2. By back washing did I remove all the DE. I ask this one because I vacuumed ~ 2/3rds of the pool and the pressure went up pretty quickly. I then back washed and finished vacuuming and the pressure didn't seem to move for the final third. This is pretty much how it worked before adding the DE.