installing new filter grids, how much DE to add?

[bjornk]

I just got the new filter grids assembly I ordered, since basically all of the old grids were torn somewhere, and with cracks on the manifold...

Now the problem I have is how much DE should I add when installing the new grids assembly? I know that it says to add 6 lbs of DE in the filter manual, but I also have probably a good couple of lbs of DE already in the pool from trying to add DE to the old filter grids after backwashing, which unfortunately didn't take and most of it probably ended up going back to the pool through the pool return... So I now have a layer of what's most likely DE and some dead algae on the bottom of the pool.

Should I still add the full 6 lbs of DE to the new grids?
Or will the new grids be able to scoop up some of that DE laying on the bottom of the pool, either just by running the pump or by connecting my Polaris 340 cleaner to vacuum the bottom?
Or do I need to get rid of the old DE somehow before installing the new grids?

If I add too much with all the old DE, I'm afraid the brand new grids get caked up immediately and I have to take them out and clean them immediately? Or if I add too little, the new grids might get clogged because of that?

Some help needed please!!

 

[Richard320]

Good question. You have no idea how much DE is in the pool? Vacuuming it up will add it to your grids.

About all I can suggest is to refill it normally, and verify pressure, then vacuum. If the pressure goes up a lot after vacuuming and letting it stabilize for a while, then you'll need to backflush and try again. If it hasn't changed much, breathe a sigh of relief. Give it about 15 minutes after recharging the new grids and pay attention to the valve positions when you take your reading, and give it the same after vacuuming

 

[bjornk]

There might be as much as 3-4 lbs DE in the pool it was dark when we did the backwash so we didn't immediately see the DE returning...

As the grid assembly is totally broken (all grids have tears, manifold cracked) and we're going to be replacing the assembly, we decided to vacuum in backwash position, from what we could read on various forums the only thing that happens then is that the grids would get muck on the inside from the vacuuming.