I'm a bit miffed and can't figure out why this keeps happening only to this one plant. This always happens the day or two after water change, so here's my routine and I'm open to trying anything at this point...
I change roughly 70% of my water weekly. I maintain 6 dGH by adding exactly the same amount of CaSO4 and MgSO4 each week, and I add 24 ppm NO3, 6 ppm P, and 35 ppm K (15 ppm from macro, 20 ppm from K2SO4) directly to the water change water.
I do water changes in the evening each week and then add micros the next morning. It's very possible the mg scale used to make custom micros was off, but here are my weekly targets:
Macro bottle: 24 NO3, 15 K, 6 P
Micro bottle: .6 Fe, .2 Mn, .18 B, .2 Zn, .006 Mo, .008 Cu, .002 Ni
Water change: 14.3 Ca, 3.3 Mg, 20 K
I feel like it's a B deficiency, but a double dose of micros the first day did not make a difference last time I tried. What's really odd is the healthy leaves in the picture were from my vacation where the weekly targets above were spread out over a little over 2 weeks... So less than half of what I usually do - 1/4 dose every 3 days :-/
Any thoughts? I'm getting close to mixing up new micros with a new mg scale, so if it's that something wasn't measured right, I'll know in two weeks :p