this is not overwatering it is either some sort of deficiency or nutrient burn. post pics and give some more background (age of plant, amount/type of nutes) so someone can properly diagnose your problem.
I'm thinking it's a nutrient burn, use just distilled water without nutes to see if the newer leaves are any better.

If the leaves are crispy it's probably a nute burn. For this prob you can get some stuff from advanced nutrients call revive or/and just use distilled water for 5-7 days.