My in-laws are interested in addressing their iron issue. They have addressed 80% of the problem by simply hanging an Ozonator in their 1500 gallon storage tank, and letting the iron settle to the bottom. However, it is a pretty big maintenance chore, cleaning the Ozonator every couple weeks, and flushing out the iron settled at the bottom of the large tank.

I believe a more-effective and low-maintenance approach would be to oxidize and filter the iron before the storage tank, and store "clean" water instead. This would stop problems with their sprinklers getting plugged with particulates, and generally just keep the plumbing cleaner. Softening would be done at the house, with the irrigation split off before. A neighbor has exactly this setup and it works very well. His well flows 10 GPM and can backwash the iron filter. The Ozonator remains in the storage tank, but needs cleaning very occasionally with it's purpose changed to sterilization of the stored water instead of iron oxidation.

But here is the problem: My in-laws well is low flow, only 3 GPM or thereabouts. They need the storage tank to supply demand. Obviously this is a two pump system. The well and pressure tank feeds the storage tank, with a second pump to supply flow rate and pressure demands to the house and irrigation.

The well pump cannot backwash an iron filter, but the storage tank pump could easily. But that is not how Fleck 7000 valves are designed. I suspect most other filter valves are not designed with three ports - untreated, treated, and backwash supply.

Is their such an animal as a three-port filter valve? Or would implementing a backwashing iron filter (backwashed from the storage tank/pump) require some tricky arrangement with an electrically-operated valve to switch the filter inlet over to the storage tank.

I would think this has been addressed before.