What is this filter system.

[Marktheshark]

The tanks say Pentair on them. They were installed on my old well system. When we moved in I drilled a new well and had a water softener installed. I'm wanting to sell these filters but I'm not sure how much they're worth.
Thanks,

 

[speedbump]

Never seen one of those before. The head is a Fleck, with a Gast air pump attached. It's probably an iron filter or possibly a sulfur filter.
I wouldn't plan on getting any money for it. If you don't know it's actual usage, it's going to be impossible to explain what it does.