any way to control pH better?

[dhanger]

Well, according to their website-

"Created with pebbles from around the world that are selected for their color and beauty."

So, if they're telling the truth, they are actual pebbles and not some composite. I can't say what the filler is, but it appears to be concrete. Seems I read once how they apply it, a layer of concrete with the pebbles mixed in, then at a point they gently wash off the concrete exposing the pebbles. Can't find that info now, so not sure I have that right.

And, I'm not convinced there is any deterioration going on there. The photos look exactly like mine (minus the black deposits), in fact it looks like there is a calcium ring exactly like mine, that may be what's making it look like deterioration.

Dan

Edit-Actually, the more I think about it, the filler probably wouldn't be concrete as the aggregate would be exposed as well. Guess I have no idea what it is, unless it's just the cement used in concrete, or mortar.