Thanks Brad, I'll try it
I 'backflush' my unit weekly for a few minutes (or hours if I forget

) before I run it, but I too am curious to see what comes out
Judging by what my pre-filter catches I expect to see some crud
For the record, I was lead to believe the 'film' in my mixing tank was from some kind of clay in the salt mix that's used as a 'stabilizing agent' of sorts. I don't know ... haven't really delved into it as it's never hurt anything