Rolled Spa glass tile scale in grout lines


Well-known member
Jun 18, 2020
League city TX
We built our pool late last summer, and added a saltwater generator this February. Since then, I've battled pH and have been trying to avoid scale. While I don't have scale on the tiles yet, I am seeing this darkening of the grout in between our glass tiles. The dry grout is usually the lighter gray color and dark when wet. This is primarily on the rolled edge spa, less so (or none) on our glass waterline tiles which stay more or less wet all the time.

I took some 1:4 diluted MA and scrubbed with a nylon brush last night. The solution bubbled and did a pretty decent job of cleaning it up. I need to redo the section I'm showing below, but it gives you a good idea of what it looks like.

What am I dealing with and how can I do a better job of preventing it?

I read somewhere to not use MA on either glass tile OR travertine, did I mess up? Is there something else I should try first? I just poured it from a cup, would a spray bottle or ketchup-type squeeze bottle be a better delivery system?

Also considering borates to help with pH. Given my pool is only 8 months old, should I hold off and see how it does over the summer or save myself the pH chase?

Test logs attached, but current levels:
FC 5
pH 7.8
TA 50
CYA 70
Salt 3400
CSI -0.26

Thank you TFP!!



Silver Supporter
Sep 18, 2020
Houston, TX
Liquid Chlorine
I'll be really curious to hear what responses you get out of this. I'm experiencing pretty similar issues with my grout lines as well. I seem to be having a general efflorescence problem on my spa spillway, and this may be part of that for me. I hope maybe you get some good answers!
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