I known this is really old but I am having the same problem. My pool is only 2 days old. I did the whole sand filter start up and it blew what looked like dirty water back in my pool and turned the entire 16x31 foot pool green in minutes. Tried it again after placing a shock and backwashing the next day and it did it again. Did you ever figure it out?
Moved from here.
Moved from here.