the medium is just basic potting soil that i have around the house, there are no added nutrients or fillers, just the soil.
your first problem is using just potting soil is really a bad way to do it If you take a look at my medium it is more fluffy and filled with air. It is actually a soiless mixture of Pete moss, perilite, and mushroom compost. Pete moss is a very good medium, perilite helps keep the soil aerated, and compost helps keep water retained and the soil moist. My suggestion is something without just soil.
I added some ferts that are also in our gardening shed (where the soil is) and that is what caused the burns. i did it once and it burned so i havent done anything since. i think the nutes i tried using were more along the lines of the flowering n-p-k ratios, rather than the vegging ratios. i have not added any ferts since the first bad experience.
Could you specify the type of fert you got. Also just to let you know using just any old fert could be very dangerous for a plant at high levels. I would really suggest you looking into some sort of mixture on the lines of 4-2-2 or 2-1-1 then possibly looking for some blood meal which is usually anywhere from (13-15)-0-0 that you can mix at a very small amount to raise the nitrogen a little. Be sure to start any fert mix at about 1/4 strength the first time. Also organic ferts will give a smoother smoke.
i dont have a thermometer in the box at the moment. all i can say is it is not too hot, and it is obviously not cold. if i had to guess id say in the range of 75-85 degrees (F).
There really is two ways you can check to see if the temperature is to high is to hold your hand about your plant and if your hand gets uncomfortably hot then you should know its to hot for your plant. The second option would be going to basically any type of store and buy any type of thermometer and tape it up around your canopy or even in your pot.
right now there is so much bush-action happening, that the inner leaves don't get much light, so as of yesterday i moved the plant to about 10 inches from the lights to promote some sort of vertical stretching. i think it is needed at this point to stretch everything out and get it growing up while growing out.
For your plant i really wouldn't worry about the ScroG method for this because it seems you already have height under control. I would suggest using Low Stress Training to tie some of those branches / leafs so the branches get more light for new growth. Also with CFL's moving the light that far would hardly get light through the canopy.
finally, i do not have a PH meter, and i know ill probably get yelled at for that one, but i made it through the first grow without, and didn't think it necessary for the 2nd. i guess if i want to play around with nutrients, it will be a necessity.
So now this makes me need to tell you to get your ass up and go to a science center near you and get yourself a thermometer and PH paper tests. You really can go and spend under $10 if you don't want to invest in going digital. As you said with nutes you will definitely need a tester.
Hope that helps. good luck