The brown film is pretty standard and will come from any salt mix really, I have heard of it from all the major ones atleast... It is just what happens to mixing barrels after prolonged use without cleaning inbetween.... alot of members have noticed this and it can be remedied easily with cleanings of the barrel inbetween salt mix batches... When I was making 60gals of RC a day I noticed it would accumilate very quickly... Seachem wasn't as bad as RC but was still present.... I assume because it mixed better it didn't leave as much residual to grow nasties on, but still wasn't pretty... The brown flake is just this, left over spoiled salt from your mixing container... it can build up on your powerheads and pumps in your mixing containter aswell so mak sure you just give them a bath....
Brian's case was the most recent, and it was the sole reason for "high" phosphates in his tank, we just had a discussion of this the other day at Bethel actually.