My pool has calcium buildup on the poolside of the spillover from the (non-heated) spa. It’s under water, right at the tile and plaster line. We had a little build up last year, and more on opening this year. I’m not clear what I need to do to keep this from continuing, or even why it’s happening. Usually keep the CA level around 300, pH seems to be on the higher end - 7.6-7.8 (I presume due to aerating by running the spillover.) what else should I look for as I troubleshoot this? I understand pumice stones are about the only way to remove the build up.