"Your spa needs to be drained, cleaned, waxed, and refilled about every
six months." -- Artesian Island Spa Owner's Manual, 2007.
I called Artesian.
"Yes. Carnauba wax the interior (lucite). Just use plain old carnauba wax like you use on your car."
And that affects the water balance how?
(Sigh) (Where do I plug in "carnauba wax residue" in the pool math calculator?)
Does anybody wax the interior of their spa?