Plant dieing fast! Yellowing between veins wilting lifeless

I have no idea what happened but this plant started rapidly declining. 2 days and it looks like its spreading to other plants.

In between veins is going yellow...

Help!

Have you been overwatering? Not letting it dry out between waterings?

Are you feeding it?

What type of medium is it in?

Coco coir perlite 60/40 mix
I watered when it was still damp to add more cmx

transplant to FFOF soil and don't give more nutes until you're sure you need to.