Thanks Doc.

I did the following:
1. Verified sand level. Open up filter, it's at approx. 11" where it should be.
2. Back-washed filter up any channels if they existed.
3. Ran 2 cups of DE through one cup at a time, at 20min. intervals. No increase on filter pressure gauge, stuff goes right through (cloudy return)
4. Verified flow rate with bucket test. 18GPM i.e. 12.8GPM/sqft with solar panels off, 12GPM with solar panels on
5. Ran filter through the night at 18GPM

Thanks for the valuable information on the flow rate. This is not a factory pump-filter combination. I already had the pump and bought the filter on the basis of the "design flow rate". I feel like I have been robbed in broad daylight. If they didn't have bogus flow rates, I wouldn't have minded paying just a little extra for a larger filter.

This morning the pool was clear, the DE just settled to the bottom. I'm sure it's DE because of the color and texture. I ran another 1/4 cup through this morning, and same thing, goes right through, cloudy return.

I then vacuumed the DE from the bottom surface. It's difficult to see, but it looks like it still goes right through the filter.

I have to admit that the DE is not from a pool store. It's a brewery grade, the datasheet states that 96% of the particles are smaller than 105um. A sand filter should therefore catch the larger particles and progressively catch the smaller particles as the DE also starts working as a filter medium.

Questions:
1. Does anyone have experience with the sand I have in my filter ? (Aquaquartz brand)
2. Does the DE trick really work ? I have a very small pool and I can see when a cup of something clouds up the pool. On larger pools a cup might will dilute and not be recognisable.
3. It would seem my filter is not working like it should. Is there a simple test I can perform to see if it performs like it should ?

Any recommendations are welcome.

Thanks,
Neels.