Nautilus FNS 60 DE Filter Questions

Like the subject says, I have a Nautilus FNS 60 DE filter on my pool. I have had the pool and filter for 8 years. I replaced the FNS grids last year. A couple of questions:

1. After backwashing the filter has about 14 psi of pressure. Before the DE is added, it goes up to over 30 psi in maybe 10 minutes. The pool is a bit cloudy but otherwise the water is good. I can backwash frequently but it does the same thing. Adding DE is a waste of $$ since it gets backwashed out 10 min later. I disassembled the filter, washed the grids thoroughly (no calcification that I could tell), reassembled, and it did it again.

2. The filter is making a continuous gurgling noise. I can see a bit of air in the clear cap of the pump strainer but I have never known it to make the filter gurgle. Yes, I bled off all the air in the filter.

3. The FNS User's Manual says to never run the filter more than 2 minutes without DE. Why? What damage will it do? As I said before, adding DE is a waste of money right now until I figure this problem out.

Thanks in advance for any advice you might have.

Chuck

I've got bad news: there's a good chance you've already ruined your DE membranes.

Go through the manual here:
http://www.pentairpool.com/pdfs/FNSOM.pdf
or here
http://www.pentairpool.com/pdfs/FNSPlusOM.pdf

Clean your grids ASAP. I'd recommend going to Ace Hardware, Lowes or whatever, and buying TSP (trisodium phosphate) to clean and degrease with.

Using your DE grids to filter with, tends to ruin them rapidly.

Good luck!