Seedling problem

I would consider methods, as that seedling didn't just randomly have problems. not enough info from a picture. looks both overfed and underfed, which is odd. This jiffy pucks are notoriously acidic and inconsistent. definitely soak those and test pH of water before use, and repeat a fresh soak until it's where you want it. if on a schedule, definitely pop more. otherwise, it's not dead, yet. I don't know the causes is but might as well try to learn if you can, otherwise it'll just happen again. big pot, small plant also causes less than ideal watering practices. is that purple in the leaves? Is it getting less than 18c at night?