I recently had an alkalinity swing creep up on my reef. Normally I like to keep the tank around 8 dKH, and yesterday I noticed the duncans in my frag tank (part of the same system) were closed up. One bad habit I've developed over the years is to watch the corals for indication of problems instead of water tests each Saturday like I used to perform. I need to get better about that. I did a quick check with my Elos Alkalinity test kit and was shocked when it hit 21 dKH. So I tested again, and it measured 19 dKH. Safe to assume it was about 20, way too high.