based on recent behaviour...
limited fertilizing -- need to feed.
been feeding from start -- stop feeding now and let it 'reset' to alower concentration in substrate, then resume, but give a bit less -- either less frequently or slightly lower concentrations.. context disctates what is best.
And no, that is neither a Ca or Mg related problem from what i can tell. those start with spots first then progress.
starting from tips in, lower on plant -- mobile, likely nitrogen... assuing pH and not lockout from overfeeding other stuff.. e.g. if you dump a ton of cal-mag on a problem that has nothign to do with ca or mg, then you will cause K/Fe/Mg and Mn deficiencies eventually, because teh Ca ions clog sh%t up, chemicaly/biologically speaking.