If you can find this Hormex vitamin and hormone concentrate
locally that's good. You can also get it at www.wormsway.com but it's a bit
pricey there.
I'm always buying sick plants on the $1 shelf or dumpster diving behind the
store. I've had luck using it mixed 2.5 ml to 1000 ml of water (depending
how sick and rootless the phal) and mist daily. Since yours has roots I'd
try 1 to 2 ml to 1000 ml. Also 40 cm isn't that long of a leaf as I've seen
white phals in the stores here with leafs that size or longer.