You are getting iron through the treatment equipment.
Did the well driller sell it to you?
What is "polyfloc" and what is it supposed to do?
My guess is it is to prevent rust stains right? If so, it will not work when you heat the water, the iron will be released and then convert to ferric iron/rust in the water.
What mineral is in the iron filter and how is it supposed to work with the polyfloc?
Why the disposable cartridge filter afte an iron filter! Disposable cartridges are a very poor choice for POE (point of entry) treatment and IMO should not be used.