impossible to solve DE on pool bottom

I have a 10 year old 30,000 gal in ground liner pool with a hayward de4820 DE filter and 1.5hp hayward pump. I started getting DE back in the pool in small amounts about 6 years ago. I was having issues with spider gasket in the valve deteriorating rapidly- I'd open the valve up and it would always be detached in the area where the upper part of the valve was not touching when in the "filtration" position during normal operation. I thought that was the issue but replacing the gasket and the pressure spring in the valve reduced but did not eliminate the DE problem. Grids, manifold and internal elbow in the filter were perfect. I basically had to let my skimmer connected vacuum run continuously to keep the bottom clean.
This year I finally got tired of that and got an electric robotic vac and even though I could find no problems inside the filter replaced all the grids and manifold, and eliminated the valve by plumbing the pump output directly to the filter. (I usually remove the filter assembly to clean the DE off anyway and figured the elimination of the valve as a potential trouble point outweighed the backwash functionality) I also put a check valve in between the pump outlet and filter inlet and double checked to make sure the internal elbow between the manifold and filter inlet was good, and there is a new o ring in the manifold to internal inlet tube. Result of all this work is that I'm still getting the same amount of DE back in the pool. I've just done a manual vac job and removed and cleaned the filter assy again and figure I'd give it one more vacuum in a few days before I scrap the DE filter and go with a cartridge system if the bottom of the pool is not DE free. Nobody at any of the pool places can help me other than to insist its a torn grid or cracked manifold or valve issue, and these have all been addressed. If anybody here has any ideas I'd love to hear...
additional info: pressure without DE is 13psi, with the specified 6lbs of DE 15-16 psi. Plumbing is 1-1/2", there are 2 outlets, one skimmer, the pump is 1.5hp 83gpm at 20'head and a DE4820 has 48 sq ft of filter area. After cleaning the filters I turn on the pump, bleed the air from the filter housing, then add DE thru the skimmer. When taking apart the filter I can see that the DE is indeed evenly distributed everywhere on the grids. I find it hard to believe that I'm still having this issue, unless perhaps I'm getting DE with some proportion of undersized grains that the filter is unable to catch that settle to the bottom of the pool. If this is the issue I would expect to see complaints on this forum and others but I don't...
tom

Hi,
I'm not the DE expert but it sounds like your pump is putting out too many PSI for your filter. IF you can establish that is the case, you can downsize the impeller on the pump to LOWER your pressure.
If you decide to change filters, consider going to a sand filter. A 300# filter should be fine for your setup, and there are lots of inexpensive tricks to have them perform as well as a DE or cart filters. Much easier to maintain, too. Cleaning a cart is a major pain in the neck.

I would tend to agree but there were no issues for the first few years we had the pool and the specs of the filter: design flow rate 96gpm max pressure 50 psi (does not specify if this is max working pressure of the tank or max pressure on the dirty side of the filter) I would expect it to be the former. I've never seen the filter pressure exceed 25psi The pump specs: flow @ 20' of head 83gpm, from the hayward chart at 10' of head about 90gpm, so it would appear the pump and filter are compatible. I do know after this experience if I DO replace the filter there is no way that I would consider any filter that uses any sort of granular material. I'm considering a pentair clean and clear plus 520sq ft cartridge filter 520 sq ft which will handle 150gpm (nsf) with a 72000 gal 8 hour turnover.The pool gets very little use, and there isnt a tree within 200 ft, but it is open all year. There is again, after the last cleaning, a good bit of DE on the bottom after my last vac yesterday. I'll be vacuuming again to make sure this was not just material in suspension; after that the only thing I can do is to install a temporary bypass after the pump to reduce the flow/pressure through the filter as an experiment, it would be helpful is some DE expert can tell me what the preferred pressures would be for my system for the following:

A:clean grids with zero DE present
B:filter fully charged with new DE
C:pressure at what should be considered ready for cleaning

If I have that info I can compare to my current situation and if I add a temporary bypass adjust pressure to what is recommended.

thanks
tom

Rather than doing a temp bypass might be easier to try to swap out the impeller as you mentioned above. Do I just order the impeller from the next smaller pump, or are additional parts required? (I've never had it apart...
)

tom