I have the same problem here in SoCal where the water is very hard in my area. I went into the water for the first time and was disappointed with the amount of roughness on the horizontal surfaces. I used my fingernail to scrape off a few of the rough spots and it was a combination of white and sandy (dirt covered scale) deposits. I had feared the worst because my SWG cell was heavily covered in white scale and not producing chlorine.

Anyhow, I want to try the method Waterbear has suggested in lowering the pH down to around 7.0 and brushing but have a few questions. No matter how much muriatic acid I add, it always seems to run high, ~7.8. That being said, I've been told not too add more than about 1/3 of a gallon of acid per day. At that rate, it will take forever to lower the pH. So...:

1) Is it safe to add more than 1/3 gallon at a time?
2) How long is it safe to keep the pH at that acidity level?
3) Are metal brushes generally safe on plaster?

Thanks in advance.