yeah, looks like nute burn. . i usually wait til about the third or so week or veg till i apply any sort of nutes, or when the plants look like they could use a little boost..
i have also heard that if you get some sand, store boughten, not from the beach or yard, and place about an inch or so ontop of your soil mix this will help reduce any fungus gnats, as the moist soil is no longer so available to them.. i am pretty sure it works well..
hope this helps some...