First of all if in fact you do have "iron bacteria". A Greensand filter will not remove iron bacteria and may very well make it worse. An Autotrol valve for a greensand filter is a really bad idea! The ports become plugged with oxidized iron and as you have experienced the venturi gets plugged frequently with oxidized iron and potassium permanganate.
I would recommend getting a thorough water analysis with a TOC (total organic carbons) test for organics in the water. You can also look for bacterial iron in the toilet tank. There will be a slime buildup or an oily type film on the water that can indicate iron bacteria. Most likely much of the iron has fouled the water softener also, especially if iron bacteria is present.
There are several ways to combat this type of iron along with hydrogen sulfide.
1. Chlorine injection / retention tank and filtration tank.
2. Hydrogen peroxide injection / retention tank and filtration tank.
3. Water Right sanitizer plus water conditioning system. This system uses KDF media and a chlorine generator to kill iron bacteria and sanitize the system during regeneration.
The first step though is to get a proper water analysis from a third party lab to determine the actual water chemistry and course of treatment. You can go to www.wqa.org for a certified water treatment professional in your area.