My apologies for the slow response.
I checked your pics and I don't think you are experiencing a Magnesium deficiency. I wouldn't worry too much about it if I were you. Just keep an eye on it and if it worsens then you may need to act. Your plants look pretty good from what I can see and yellow leaf tips are not typically a problem (so long as it doesn't worsen). Some people claim that yellowing tips is nute burn. I have a couple of strains that get yellow tips no matter what I do, so it could be genetic. All in all, your grow looks pretty good. Happy Growing my friend, and don't hesitate to hit me up if it gets worse.