because of multiple types of symptoms, i'd lean toward lockout or pH issues. Any time you see things that lead to multiple "right" answers on your leaf chart, it's likely something else than all of them.
Light burn doesn't look like that. Doesn't start on tips. Only see it at top (except extreme circumstances.. if intense light is hitting a lower area but nowhere else.. very unlikely but could happen outside due to shade or something)
Take it weasy for a bit. If you have been feeding consistently, that's probalby why it's a bit slow.
if your behaviour doesn't match up with my assumption, then ignore me. Just because the others, even if same strain, can handle more doesn't mean this one can.
don't add stuff yet... See if ph-only clears it up or at least stops progression.. then, you know i'm right.. if it takes an immediate nosedive, you know i am wrong, lol.