Yeah, def. nute burn. You could have done it in MG soil, but not with MG soil + MG nutes this early in the game. Also some of the stuff in the MG soil, such as the micro nutrients, is designed to last 16-18 months. The regular fertilizer in the soil is supposed to last 4-6 months. Usually flushing heavily just releases more nutrients.
I would either use MG as MG recommends and how they designed it to be used or transplant it into another medium so you can grow using methods your more familiar with. There's lots of good info on MG's website, just have to search around a bit.