I have DE in my pool and I can't find the reason why. I have been taking care of my pool for 16 years. Recently, I had some DE in the pool and I was sure there was a hole in a grid. I had replaced them the last time I cleaned the filter. So, I opened it up and they all look just like new. After cleaning the filter 3 times, each time thinking that I missed something, I still have the same problem. Then, grasping at straws I thought maybe something was going on in the backwash valve and because the filter was old (Purex SMBW 2060) and parts are getting scarce, I bought a new Pentair SMBW4060 and I have the same problem. It takes a couple of days but I get a coating of DE on the steps. I am using the same quantity of DE as I have used for 16 years. Does anyone have any ideas? I would really appreciate anyone who may have had this experience to give me some help.