Help, something very wrong with leaves

A while ago this was localized to one branch that wasn't receiving much light so I ignored it because I thought that was the problem. Many weeks later I noticed it had started to affect bottom & middle fan leaves and also some bud leaves as well.

I suspected mg deficiency but I thought that only caused a yellowing and some rust spots, and not start off with some kind of necrosis. I've used some epsom salt (1 tblsp/gal) regardless in my water.

My soil PH is 7 and the temperature is kinda low, probably 50s, but I don't know exactly.

I can't find anything like it on the internet. Please help.

Looks like mg deficiency to me. MG absorption drops off at higher Ph's though, try shooting for a lower Ph (around 6.3), and are you using gardening epsom salt or bath epsom salt?

Your temps are a bit low, but that should just slow growth no cause deficiencies.

I just checked out the box and it looks like bath, 'soaking solution' and such, and now I feel like an idiot. I've watered with the solution once, am I fucked? Perhaps a flush is in order?

Perhaps? Hell yeah a flush is in order!

yeah dig up the topsoil that the actual salt is sitting on top of then flush.

There might still be hope :/

I water from the catcher at the bottom so I can't really dig it up. I'm going to flush anyway. How will I know if I solved the problem? Everything on these leaves predates the epsom salt issue.