I dont think you have a mag problem unless it to high. Most of the time if mag is low it keeps your ALK and calcium low and wont let it go up that high but could be wrong
I agree, check your mag. If you mag is way off I would recommend getting the mag in check. This could possibly get your calc and alk closer to where they need to be.
Honestly I would not worrie about it too much. Being that most of us dose daily, without dosing the levels should drop over a short period of time. Again, check the mag and it might fix the issue. Also, if you want to drop the levels, small water changes over the next couple of days would help the process.