@gordongecko, the plant was having issues from day 1 of its life as a seedling -- pale with ever so slightly curled-down leaves. But definitely not this pale. I can't tell exactly how pale because i am red-green colorblind and find it supremely difficult to distinguish shades of green vs brown vs lime-yellow. So it is entirely possible that I just didn't see the early deficiency.
I thought it was overwatering, so i dried her out. Then more problems happened, so i fed her some calmag, foliar MgSO4, and about 350 ppm of all-around nutrients. Then it got worse still, so I have been keeping with a very moderate feeding and mag sulf foliar. No idea how the toxicity happened - all three plants were given the same medium, and the other two are doing fantastic in comparison.
But it is possible that the soil load was too hot due to poor mixing, and/or too dense and didn't drain at the same rate? Then compounded?
I can see purple though, and the stems used to be almost entirely purple before cal mag and mag sulf. They cleared up but the rest went to shit lol
Thanks for the concise summary of symptoms vs. causes, gives me a solid idea of how bad it is
I am not that experienced with plant health issues - I must have been lucky in the past, no issues other than occasional nute burn, wind burn, light burn, and, of course, overwatering when i first started...