How many pounds of AA did you use JUST on the last AA treatment? Just curious.
With 26,000 gallons, IMHO you're probably looking at 3 bottles of Jack's Purple Stuff for the initial dose and roughly 24oz additional each week (Yes, I overshoot the recommend #'s a bit, which is why I'm recommending more than what you might read on the bottle itself). Jack's isn't super cheap, but at this point, if you're like me, you probably don't care and just want issue addressed so you can enjoy your pool.
Iron bacteria is more common if you have a well (another crappy issue I deal with as well, as the well has to be shocked/chlorinated 2x a year to treat the bacteria) as it leaves a filmy-slimy (dead skin-like) coating along the water's edge. I have not really seen this in my pool, though I definitely see it in the back of my toilet tanks if I let my well chlorination go too long between treatments. If you don't have a well, I doubt you'd have iron bacteria (just $.02).