Ok, so I followed the rules for adding a small amount of DE to my sand filter. After and extremely thorough backwash, pressure was reading 16psi. I added small amounts of DE until pressure increased to 17psi. I kept checking pressure regularly throughout the evening until bed time. At 10pm pressure was only at 18-18.5psi. At 4am on my way out the door for work, I checked and pressure was 25psi. Ok, time to backwash again, as I read this is normal when you first put DE in filter. Maybe even for the first few times. However, did have time to backwash then as I was heading to work so I just turned the pump off. Came home for lunch and was going to backwash, but just because, I turned pump back on to verify pressure and it was only at 18 psi again. I backwashed anyway and added more DE to filter. Same thing happened again. Pressure slowly increased up to about 25 psi over the next 16 hours or so, but again no time to backwash. Turned pump off at 4 on my way out the door for work. Came home at lunch to backwash, and again just to see, turned pump back on and it was only at 18 psi again. So this time I left it alone. Been running all day (since noon) and pressure is staying at a steady 18 ish psi.
Why would it increase to 25, but then after having pump off for several hours drop back to 18 once the pump is turned back on? Should I backwash again, or just see if it does this again overnight and tomorrow?