RDspaguy
In The Industry
You may know that, but I'm obligated to do what they say on a public pool (1-3ppm) or spa (3-5ppm). Private is another matter. But if I was on the job I'd say your fc is WAY too high (and maybe ph too low), and is likely the cause of your rusting stainless. That may not be correct, but it would be my guess walking up on it with rusty stainless and 12ppm. I'd then ask how frequently you have to replace your heater and pump seals, and check your jet inserts and gaskets for damage. But I'd also say I'm no chemistry expert and can only tell you what works for me in my spa. Which, incidentally, is NOT EPA approved, and rarely sees 10ppm without people in the water, and never with.government public rules & traditional pool care says 1-3ppm is ok & 10ppm is shock level without taking into account cya or no which we know is not fully accurate.