It's not clear from your municipalities' report whether they use straight chlorine or chloramine for disinfection; you can call them if you want to verify. If you've used your RODI system for a year without replacing the cartridges, and it only had one up-front carbon cartridge to begin with, there's a decent bet that you're getting chloramine through your system. At any rate, it's a pretty cheap set of
test strips to a) test your incoming water, and b) test your product water. Keep in mind that while you may only have made 700 gallons of product water in a year, at least 4 times that amount will have gone through your carbon and particulate filtration.
You didn't answer the cleaning agent question, but be aware that certain cleaning products are absolutely deadly to aquatic organisms in very small concentrations - benzalkonium chloride/bromide being the most glaring example.
Another couple of thoughts:
You mentioned a refractometer; it would be worth checking it against a LFS's reading to make sure it's accurate. If you've a digital refractometer, you're probably OK, but the "look through it" types can be fairly difficult to get accurate readings from.
You also might want to verify your temperature measurement device; the best comparator is an analytical grade mercury thermometer, but those are getting hard to come by. Failing that, though, you might consider purchasing a second indicator and checking it against your primary one; there have been a few examples where someone's tank temp was found to be WAY off. One other aspect of this is temperature stability. If you're using an Apex or other means of recording the temperature and it doesn't show significant (>2 degrees over a couple of hour's time) variation, you're good. But I mention this because I just pulled a brand-new Eheim Jager out of the box, and it has a temp variation of over 4 degrees F.
I think you can see where we're going with this. You clearly don't have a contaminant that would cause problems that ICP can measure. That doesn't rule out the use of an environmental toxin like the afore-mentioned cleaning compound, but if you or someone in your house isn't using that, there's not much else that could be having a direct toxic effect. Since all of your corals are affected, it's doubtful that your alkalinity stability (or lack thereof) is causing issues, since zoas in particular aren't known to be overly sensitive to this parameter.
That leaves certain environmental parameters, such as temperature, salinity, gas exchange, light intensity and (possibly) nutrient swings.
