Are you only using Alk, Ca, and Mag to dose the tank? Are you also using a pH buffer? Using both Alkalinity and a pH buffer will shoot your Alk up.
Small water changes wont do much to lower the levels since new saltwater typically has elevated levels of Alk, Ca, and Mag. I would do a 20% water change and just let the tank drop down on its own. If you cause too big of a swing (up or down) with any of those, it could stress the corals even more. Make sure
Hope this helps.