Use
I used standard IO for years and my brutes are clean.
A small amount, 1/8 of a cup, of rox and it will pick up the the residue.It leaves a brown residue and will have scale build up over time. I'm not sure of the cause of the residue but I think I remember @Randy Holmes-Farley saying something about clay but my memory is bad. I read that he is using IO on his 1% per day AWC system.
I used standard IO for years and my brutes are clean.
