big fuck ups, i left the res empty for like 2-4 mins when changing the solution and she was super sad, thought I had killed her! Do not leave res empty for any amount of time. also sorry for the yellow photos i figure out how to correct it in the later photos. going to take a break and upload the rest later today.
i concur with your diagnosis -- ph fluctuation
if it continues and spreads watch the pattern sometimes light burn starts between the ribs of the leaf like that as yellow and spreads
especially if it gets suspiciously even patterning -- ph spots are usually irregular spots
@DojoGeejer, never used it for that purpose but i am a big fan of potassium silicate in coir, makes much stronger plants
it will definitely make the roots of any of your plants less susceptible to shock from any source so it should work to help against ph shock i suppose?