| | Re: Plants melting in new 40 gallon tank..
I'm not sure if the lighting is enough but i'm guessing you know the requirements of hc. Anyways, it's most likely because the HC you ordered was grown emersed and since the conditions of your tank is radically different than the one it was grown in, it has to convert to submersed. The crypts may or may not have been grown emersed, but regardless crypts melt all the time when put in new water parameters, it's just how they are? it's called crypt melt. just leave the rhizomes in the substrate and in a couple weeks new leaves will grow out again.
as for water params... water params are only really important for livestock, not so much for plants. water params only affect plants if you're low on nutrients, or if your params fuel algae, but regardless those are problems that come later.
if the HC is dead like completely dead, then maybe try floating some on the surface until they convert? but otherwise either transition it slowly from emersed, or make sure your tank specs are good enough and just try again with HC? if you still can't get emersed HC to convert, just buy it from a seller in submersed form.