Calcium Scaling Above Water Line On Both Sides of Waterfall Spillway


Silver Supporter
Bronze Supporter
Jul 13, 2015
Huntingtown, MD
For a month or so, I have had white scaling forming along the horizontal tile grout lines on either side of the spillway from the waterfall Jacuzzi into the pool water below. I will assume for now it's from splashing on to the tile. It's not a lot. YET! But I would like to get ahead of it and remove it soon. Tried with my fingernail last time I was in the pool, no dice. I read the article on Scaling in Pool School...left me with the Question: how? Pumice? WIll that scratch the tile? What about a very low concentration of muriatic acid? 10% acid/90% water....or will that mess up the grout too? Other chemical solution? For the most part, I have kept the balance and the CSI in really good shape since opening the pool in April...before it appeared in May....usually in the -0.3 to +0.3 range. CH is about 275 (not 350-450, should I raise it, which is counterintuitive for this problem)....And one thing I am very happy about is my "Ph Bounce" seems to have gone on vacation, it's much more stable over time this seasons than past......and my TA has been consistently around 70. CL with SWCG will usually be in the 4-7 range. Just finished SLAM this morning (clear clear clear water!), what I had failed to do since the opening was kill ALL the algae...

See pic. Red lines point to the most prominent locations where scaling occurs, parallel to the water line.





Gold Supporter
Apr 3, 2019
Like you said already, pumice stone (do a test area first) will remove some of it. A dilute acid solution will help to remove some that the pumice won't get.


Silver Supporter
Sep 17, 2017
Silicon Valley, CA
I've used pumice stone and dilute acid (about 4:1 or 5:1), but have also used the tip of a flathead screwdriver to pick off the kind you have. But be careful. Some people complain that it can scratch.

You are right that you need to nip it in the bud. More scale will nucleate faster on what has already formed. With this problem and an SWG, I work to keep my CSI on the negative side of zero. If you don't run the spillover constantly, you can add MA directly to the spa to keep its CSI a little lower than the pool (remember, CSI will raise when you heat the spa). I regularly drive the spa CSI to -0.5 or so before running my daily spillover. I think this helps to keep the wall a little cleaner.


TFP Expert
Mar 2, 2011
Most likely, it's efflorescence, which is water bleeding through the wall from the other side.

As the water travels through the cement, it picks up calcium and deposits it as the water emerges from the wall and evaporates.