We have a waterfall, but I am not sure what type of rocks were used. It wasn't specified in the contract, and at the time I just assumed they would use the "right" kind. And I think they did. We've had the pool for three pool seasons now and used the waterfall alot. We really only have a few spots of small staining just under the waterline tile below the waterfall - maybe three inches worth of stain below the tile in the spots where it has happened. I have never even attempted to clean it off as it doesn't bother me (at least yet ). I guess a few times we've had some very small "rock chips" that have ended up in the pool after running the waterfall but very seldom and not any significant amount so a tiny bit of erosion only. Calcium has not been an issue, and I'm not having any chemical issues. Sure, the ph goes up a bit if I run the waterfall and/or other water features alot, but I just throw some acid in - no big deal. I've attached a pic of the waterfall and a stain that also shows a closeup of one of the rocks. Maybe someone can tell what kind of rocks I have!