Is this scale?

[Mikel]

4-year old pool had ultra-white plaster over gunite. It has a fountain in the spa with a waterfall into the pool, so my PH is always pretty high, usually around 7.8 or 7.9. I didn't know any better, so I left it there. Other levels, other than cya were always in normal range. Hardness was around 400 or so prior to partial draining.

I always have scale on the surface of the rocks on the waterfall, but I recently had to drain half my water to lower CYA levels, and the walls looks light to medium gray over most of the whole surface. I wasn't sure if this is dirt buildup from lack of brushing or a thin coat of calcium scale on everything.

You can really only notice the color in a couple places on the bottom when the sun isn't directly shining in the pool, so I guess its not a major problem, but annoying. If it's dirt, I can acid wash next spring. But if it's scale, from other posts on here, it looks like there are some simpler solutions.

Also, in all the acid wash topics on this forum, only one person asked how to get rid of the water in the bottom when done.. Another site said to add 1 lb of baking soda for every gallon of acid used during the process prior to pumping into a storm sewer...

Thanks in advance, Mike