I don't run it that high because running at 9s gives me time to catch the alk slowly raising or lowering and allows me time to fix the issue. a lot of websites have suggest alk levels of 8-12dkh so an every day test at 12 would be ok. It would be risky not smart choice though because if it raises much higher there will be issues. One alk reading of 12 doesn't mean much to me. A graph of all alk readings at random times over months means more because corals hate the fluctuation. If the only thing you are doing is water changes I would like to know how large the water change is and I would do an alk check after. I feel smaller more often water changes are more appropriate because the alk,PH temp etc won't spike. There are 1000 more factors that can cause issues. LEDs were my first issue (learning curve). They were brand new and I had them cranked up. LPS doesn't like fried. It also could be improper/faulty test kits, a brand new coral with acclimation issues etc but I don't want to get off the subject