Nitrogen burn or Nutrients Deficiency??

Hi guys
I've got this little one planted for 1 month now and here's the problem: The first and second stage of leave have died and now the third is turning yellow...

Is this nutrient deficiency or nitrogen burn?

To be more specific, the set of leaves that ided are the first one-leafed set and first 3-leafed set...

I started to use a 15-15-18 fertilizer but i didnt put alot.. my girlfriend kept telling me that i have to be careful not to burn the roots so i didnt use much...

thx for the help

that's a defiecency, the plant is pulling the mobile nitrogen and other mobile nutrients from the lower growth to feed the new growth, if it had been too much you most likely would have seen it start at the top and work it's way down.....

I agree ^ that's a defiecency. What kind of lighting are you using?

What lights are you using? The plant seems to be very stretched out.
Are you by any chance watering will well water?
What is the pH of the soil?

During day, the plant is in front of a large window and receive a full load of sun, when the sun sets, i use a linear fluorescent lamp. I know it's bad...
For the ph level, i have no clue
I use tap water that i left standing for 24h hours before use...

My goal was to put him outside but it's still too cold

And is the fertilizer that i'm using good or bad?

Is leaf feeding something you guys would suggest later on?
By leaf feeding, i mean spraying a fertilizer diluted in water directly on the plant...

If my fertilizer isnt any good (currently it's 15-15-1 What should i buy?

I would suggest not using that fert at full strength until you get the plant into some good light.

Even at 1/4 strength you're plant may end up as a single stem 6 ft tall because under low light conditions (like you're trying to use) ANY nitrogen you use will make the plant grow more stem that it will leaf.

good luck

bt dt