blackjack - day 12 - nutrient problem???

Hello, this is my first grow. This plant is 24/0 light cycle under 400w MH hanging about 2 ft. above the top of the plant. Haven't used any nutes yet but seems like the yellowish/brown matches up with some of the images showing nute deficiency.

Have them in regular Scott's soil and did have a gnat problem (hence the rocks on top of the soil). The coloration of the plant (yellow/brown) started a few days before I noticed gnats and added the rocks.

My growroom is well ventilated @ 85 degrees farenheit and ~50% humidity. I have CO2 on the way (fizz tabs) but wasn't planning to start using them until closer to flowering.

I water it about every 1.5 days after the soil in the jiffy pot is completely dry.

Any feedback will be much appreciated and welcomed. Thanks for having a look.

all normal at this stage. wait a couple of more weeks b4 feeding it anything and when you do start at 1/4 strength

Looks ok to me. If you continue to see burning or yellowing you might consider switching soil. I've always had great results with FoxFarm Ocean Forest. Also make sure your water is PH adjusted or it will lock out nutrients.

thanks folks

I'm picking up some FF ocean forest tommorrow from a local hydro shop, cant wait to give it a try. I've heard nothing but good things about it. I would definitely switch to that or something similar if you continue to have problems. Good Luck!