CA of 367 a problem?

Initially, I think not. The day this measurement was taken I also had a pH of 8.2, and TA of 136. If it were to be trusted, the Saturation Index was measured at 1.1. I have a plaster-bottom pool of about 15k gallons.
I had not added the weekly dose of acid, so the pH was squared-away right away, but the chemical-seller saw an opportunity to sell something called "Suspend M+S", a stain and scale control. But I have got a patch of discoloration that doesn't brush off, so I'm thinking of trying this stuff. The cost is about $12 a quart and they recommend 1.5 quarts.
Does this make sense?

I believe that Ca for plaster pools is to be 200-400, so I don't think 367 is a problem for you, unless you're using cal-hypo for chlorination. If you are, I'd switch to a non-Ca product.

Janet

You can try rubbing some Vitamin C tablets crushed in a sock or stocking on the stain, or if you have some ph down you can use that instead - if it lightens up it is a metal stain if it stays the same it is probably organic. They are telling you to put a sequestering agent ("Suspend M+S") to bind with any metals that are in the water. You won't need this if the stain isn't from metals.