Fungus, bugs or my bad?

This is the second plant that we have had develop burn like this on the leaves. At least I think it's burn. The leaves turn brown on the outside edges and crumble at the touch. New growth continues to come out the top nice and bright green but all the leaves below are dying off. What did I do, or what do I need to do?

Nutes?
PH?
What is your lighting?
Temp and ventilation?

Looks like maybe a PH issue??

I would say nutes. But it could be anything. Check the plant abuse chart. See if it helps. https://www.rollitup.org/view.php?pg=faq&cmd=article&id=37