Vacuum - DE Returns To Pool

[vregister2]

I have been reading various posts and this forum has been very helpful. I have gotten my water cleaned and all chemical test are good. However, after I vacuum and backwash the DE returns back to the pool and spa and settles on the bottom. I'm not sure how to vacuum to waste. Here are my specs:

In ground "plaster" pool and spa
Nautilus FNS Fiberglass DE Filter - Two Position Slide Valve to backwash (manual states "do not vacuum pool while backwashing filter")

After I backwash I do put in more DE maybe I shouldn't? Not sure.

Thanks for your response

[Donny]

Here is what the manufacturer says about this problem:

It would be best to vacuum up the D.E. in the pool and then add D.E. if you know how much is in the filter after you do this. If you don't, then vacuum up the D.E., backwash the filter, and add approx. 80% of the total amount recommended on initial filter D.E. start up. Clean the filter grids well and look closely at them for any holes. The slightest hole can allow D.E. to go through the filter. Also, the manifold at the top should be examined closely for any cracks or holes. Lastly, check all pipes to see if their associated o-rings are ripped, torn or missing. Replace as needed.

You cannot vacuum to waste using the 2 position slide valve. vacuum the DE up and it will stick in the filter.
You have to add DE after each backwash.