I have had a Hayward DE Filter for about 20 years and it's worked flawlessly. About two years ago when the grid was removed to be cleaned all of the DE powder was accumulated inside the filter panels not coating the outside. As a result they could not be be cleaned. I replaced the grid and the same thing happened the next year. I replaced the grid again this spring and the pool is not filtering so I suspect the same problem. How is it that DE would be flowing inside the grids instead of coating the outside? The only change I can think that occurred at about the time this problem started is my Hayward multiport valve was replaced. It is the exact same valve as was previously on the unit except the discharge pipe is on the opposite side of the valve, could that make a difference?? Is it somehow possible that instead of the water flowing into the tank through the filter grids and out to the pool, the water is flowing into the filter grids then into the tank and out to the pool? My pool guy is totally perplexed. Help!