I'm sorry for the delayed response; had a emergency come up and I didn't want to give bad information. Been running it on recirculate only for 48 ours (needed to keep the water moving to circulate the chlorine) and it's running just hard as minute one. It's got to be something in the filter with the new grids. I've been responsible for running pools continuously since the late 70's with some of those years being public pools including municipal pools with hundreds of thousands of gallons, ton chlorine gas cylinders (lots of fun putting on the full face gas mask to work on in August), and three sand filters that we would drop down the access port to crawl inside of to work on. Been through many of the fads with copper ionizers, baquacil, zeobrite/zeosand, etc. I'm really, really, not trying to be a braggadocios Rear here (because I'm obviously stumped in this situation), just trying to give some context when I say that the conditions of the pool were not good, but there is no reason that it should be acting like this after only 15-20 minutes, especially with no DE whatsoever. When you backwash, there is nothing in the sight glass or the the water output, just clear water. There's got to be something with the new filter grids or the way that I put them together/installed them. Mechanical obstruction maybe? Thanks!