I would start by replanting into fresh soil with some worm castings and perlite. It looks to me like maybe your mix has gone anaerobic which would also affect ph…How long has it been in that same pot?
May be time to find a good top & clone it. Then try a remedy recommended by one of RIU's helpers on the plant in these pics.
Long story short.. Take a cut, then get to trying to fix the issue.