Help

Hi guys I know this may be a little problem leading to a big problem. I have switched to 12 / 12 about 3 weeks ago. I have given them cal mag. Vitalink buddy and some other cheap fertiliser. It's not high in nitrogen probable about 3. The p and k are about 7 to 10 each so I know I should probably be higher but I don't want to fuck the plant up. Its just a little experiment for a nice smoke. I basically have done it the cheap way under a 250watt red spectrum Cfl with reflector in a cupboard. I have just noticed some little bits on a few leafs turning dodgy. Could anyone help. Is it the start of nute lockout? I haven't in my opinion over fed I have probably under fed but not by much I have not given the full dose as stated on the bottle as I didn't wanna nute burn em. But I have noticed the ends of some leafs did yellow but not much at all and on the very tip so slight nute burn there i think. I haven't lost any leafs due to lack of light ect. Just wondering if it looks fine. Getting kinda stinky now for only 3 weeks in aha I have had to hand my light to the right of the top of the plant too due to hanging issues but seems to be doing fine cheers guys