A little confused. any advice or info would really help

Hey guys,
I have a few girls about to enter their 3rd week of veg (currently 19 days after sprouting)
about a week about i began to use bio-grow after i was told by the guy at the shop to use it for the entire life cycle. its a light ORGANIC nutrient solution NPK of 8-2-6). Bottle says use 2-4 ml per L of water. i used 1 mil per L. i then noticed some plants starting to get a slight nute burn. i immediately stopped with the Bio-gro and started doing some research cause i thought it was very hard to nute burn with organic nutes. i realized that the soil that i bought has these little yellow nute balls. im pretty sure thats the problem. the plants look rather healthy. lots of growth.

my question: since my soil already has these nute balls, and two plants already showed signs of nute burn, when should i start to use the bio-grow again. i read most people start with nutes after week 3 of veg. thats in 3 days for me and i dont know if i should wait longer cause of the nutes already in my soil or if by then the plants will be big enough and old enough to handle the extra nutes.

What type of medium; soil or hydro? SOIL
What brand and type of soil? not known. seems good. lava rock, sponge and all sorts of good stuff. also has little yellow nute balls.
Indoors or outdoors? Indoors
What strain? Trainwreck
How old are the plants? 19 days since sprouting
What type of lights and how many watts? HID. 400W HPS w/ cool tube
How far from the lights? 24 inchs
What is your watering frequency and source of water? tap left out to aerate. PH down to around 6.5
What, how much and when was it fed? NPK? used Bio-Grow (8-2-6; organic; used 1/4 prescribed dose
What is the medium/runoff pH and PPM if in hydro? not totally sure. have crappy prong checker but i dont trust it.
What are the temps and humidity in the room? around 80-82 w/ light 70-72 without
What size pots? not sure, not small tho.
Any bugs? Look real close. no bugs
Any other pertinent info? I think they're pretty healthy. a few were transplanted 7 days ago and it went well.

thanks for any advice and +rep for those who help.

bump...

i cannont transplant into a diferent medium. im pretty comfortable with this soil. other the then nutes, its been awesome. well draining yet holds water real well. i also dont live in the US and cant just go to home depot to get some soil. im basically stuck with what i have.

my question is still if i should hold off on using the bio-grow for a little longer. as i said, most people say to start with nutes after week 3 of veg. but those people dont have nutes in their soil already. when should you start if you already have nutes in your soil.

as per your advice with the lights. i tinkered with the height for a while. i live in a very hot area of the world so i cant get too close without the temps rising to much even with the cool tube.