Thanks for all the replies - here are the answers to your questions and more of my own questions:

I have an inground plaster pool, about 18,000 gallons

My fill water has a calcium level of only 20 so I have no idea where all this calcium came from!

I have not really tried anything yet for the stains, except for pumice stone (lots of elbow grease required!!) - do you mean for me to try ascorbic acid on the tiles or on the plaster stains?

I know I can partially drain and refill to lower the CH, but do I NEED to do that? (I'm a little worried about getting everything back in balance with new fill water.) Is the CH causing the problems or can I just leave it be and concentrate on the alkalinity? I will do the partial drain if it will help though...

And what about the dirty looking, stained plaster - is that something I need to deal with more aggressively? Is it something I have to treat specifically or will changing the water chemistry help? Is it a sign that something is terribly wrong?

I will try to lower the pH and TA down even more to see if that helps. My TA was back up to 130 this morning, but pH was still 7.4

Oh, and Salinda, yes, I regularly have to soak my cell with muriatic acid - the deposits on it get so bad!

Thank you!!!
Nicole