I have a Hayward 210T sand filter, and it seems like small particles are re-entering my pool. For example, I vacuum one day and the next morning it seems like some of the small gravel particles I vacuumed up are back in the pool. The multi function valve is a Hayward 711 and I also replaced the spider gasket on that. Today, my filter pressure was at about 20, so I decided to do a backwash. After doing the backwash, I ran the rinse cycle for about a minute. Then I put it back in filtration mode. It seemed after this, that the problem was exacerbated as I noticed several small pieces of debris under the return line. The overall pressure in the filter has gone back down to 12, so the backwash seems to have helped. Is it possible I have a mechanical problem with this filter system? The pool has only been up for about a month, and I am new to this, so it is entirely possible that I've done something wrong, or perhaps I am a bit too concerned with ultra clean pool. The water chemistry is very good, and the water clarity is very good. I just notice, what I think, to be a quick accumulation of small debris on the bottom of the pool.