Zeolite is known to absorb and remove ammonia from water (not that this matters in a pool since virtually no ammonia will be present when there is chlorine) and I found
this link supporting removal of some heavy metals (lead and copper) using SOME forms of zeolite, and I found
this link referring to absorption of iron. Zeolite is a type of cationic (positively charged ion) exchange system, but like all such systems they have different selectivity rates and capacities for different types of ions.
As teapot has noted, zeolite doesn't work very well in SWG pools because the higher sodium levels in such pools significantly lower the capacity of the zeolite since sodium competes with other ions for binding to the zeolite. In fact, one "recharges" zeolite by soaking the material in a high salt (brine-like) solution.
I can't comment on how quickly zeolite would remove the iron nor on the capacity requiring recharging of the zeolite nor on which kinds of zeolite would be best for that application. It probably makes more sense to use a known ion exchange resin filter designed to remove iron for the water during a fill and on the fill line for water replacement from evaporation, though during the initial fill there could be a lot of recharging of the water filter required (so having water trucked in for the initial fill might be better).
On a related Zeolite topic, there are some tests being done at
NSF International testing Zeolite's claimed ability to reduce monochloramine. I'll report back on those results after the tests are completed. I am skeptical given what I know of the fundamental chemistry, but there's always the possibility of catalytic acceleration of reactions (monochloramine --> ammonia) or direct absorption of a rare monochloramine ion (NH
4Cl
+) by the Zeolite.
Richard