My guess is only about 75% of the junk gets eliminated when you backwash. That is exactly why I never backwash my DE filters. I disassemble and clean them twice a year, once in the spring and once in the fall.
I can do this because those pools have variable speed pumps running at a pretty low RPMs most of the time. Not sure what type of pump you have as I don't see it in your signature.
Single speed pump. I was told buy the local pool store to backwash when my psi doubles, its normally 10psi when it hits 20 Ill backwash. I'll break the filters down 2-3 times a year for a good cleaning and inspection.
I have a Multiport Valve in my pool equipment and I usually Backwash with the following method:
- Backwash position. Run pump for a few seconds until Sight Glass begins to clear.
- Rinse position for ~10 seconds.
I repeat these 2 cycles 10 times. After 10 cycles, I see virtually no DE present in the Sight Glass.
I don't know the % of old DE & debris/particulate removal with this method, but I track my PSI readings and since the last time I pulled my DE Grids for cleaning in Sept 2013, I haven't accumulated much PSI rise (the amount of 'best-case' starting PSI to PSI after reloading with new DE). My PSI rise has been about 1-2 PSI since Sept '13.
I load new DE using the "80% rule", by reducing the new DE amount by 1 DE measuring scoop. As an example, my DE Filter calls for 3.6 Lb DE (seven .5lb DE scoops), so I only load that amount after cleaning or installing my spare Grid Assembly. All subsequent DE loads are done with six .5lb scoops.
I also monitor my flow GPM with a Flowvis® Flow Meter to provide an additional measuring tool with my PSI Gauge to let me know when a Backwash is required for my pool.
I don't use the 25% method but am aware it's the forum recommended procedure and am not disputing that recommendation.
I'm just passing along my DE pool filter experiences since I switched to the TFP pool water method in June 2014.
The effect of the basic TFP methodology (FC/CYA ratio & Bleach dosing) has been amazing to say the least, resulting in consistent crystal clear pool water & I haven't 'shocked' my pool since that date, and since adopting the method, my Backwashing frequency (& pulling the Grids for cleaning) has decreased significantly.
I average ~3-6 months between Backwash cycles. Here's my Backwash dates since switching to TFP dosing in June 2014:
Based on my pool's DE Backwashing & filtering experiences, I haven't seen the need to pull the Grid Assembly for seasonal or timed-based cleaning. If I was seeing indications of that required, I wouldn't hesitate to perform that maintenance as I have a spare complete Grid Assembly (with Manifold & base assembled) for a fast swap for troubleshooting or cleaning.