12 is a bit high, I keep mine around 9. cal 450, mag 1400, and dkh 9-10. U need to keep proper balance between all ur params though, cal / mag balance should b around 1:3 with dkh around 9-10. Seems like those params with a salinity of 25-26 do the best for my corals. Keeping ur salinity, alk, cal, and mag all in balanced ratios will help the most!