Hi, chem geek. Nice to hear from you. I've been lurking for awhile and have read through both threads. I appreciate the info very much. The minerals in the pools are mostly iron and a bit of arsenic. The facility is more than a hundred years old, so there is a lot of folklore and imagination in what our guests hear. The pool itself is very old, and the plaster is permanently stained brown. That's the way the owner wants it...rustic (rusty?).
The pool is heated from a flowthrough from two hot springs (109 and 131 deg F), so there is a limited amount we can do with the chemistry. I (being colorblind) have a LaMotte ColorQ test kit. Our pH is 7.5 +/- 2, which is fine. TA is generally over 200, CH very low in the 20s. We chlorinate with trichlor in erosion feeders; the flowthrough keeps our CYA below 30.
I was thinking about looking into automated chlorination--currently we have to test every 4 hours. You folks have made me think twice about ORP controllers, though. Are there other options?
We also have 10 mineral baths which are not treated with chemicals, only ozone and UV. The guests think it's good that we don't add any chemicals; I don't. But we do empty and clean them nightly.