I read your description in your initial post. Go open up your toilet tanks and take a picture and post.
Wish I wasn't, but I am very fluent in iron from well water. And what it takes to reduce/ remove it. Would not be surprised if you cut open your horizontal water delivery pipes and a very thick layer of iron in the pipes.
Cartridge filter is not a solution based on the information you posted in this thread.
That was my take as well. What he's describing cant be scrubbed by a softener and a cart filter wont last very long.
It all starts with a test, outside of this it's guesswork.
OP - what type of sediment filter are you using in your 2.5X 10? Pleat, melt, string?
How long before changing out?
You cant get a really good sediment carbon combo until you go with a 4.5x10 or 20, but there are some good options for string filters.