Yeah major nute burn, think it's toast now so I'd start a new seed. There are a few here using Megacrop so I'd take a look at their grow journals. But average is 1 to 2 grams Megacrop per gallon for seedling stage then working up to 3 to 4 grams per gallon vegetative. Some are running just Megacrop for the whole grow, then few others are backing down the amount of megacrop when adding P/K boosters for flowering.