they look very good ... that tip-burn probably IS from the MG soil, but since you made it thru the seedling stage, they should be fine ... young, tender seedlings usually don't tolerate ANY amount of fertilizing, very well ... photos look like some green specks of algae on top of your soil ... true ?? ... if so, spray with some diluted hydrogen peroxide ... can't give you any ratios, I just splash some into water, not real critical ... be careful you're not over-watering ... spraying the leaves in un-necessary, unless you are foliar-feeding (possibly the reason for your algae) ... :thumbsup: