is this a sign of over/under watering or lack of nutrients?

Im a bit of a noob grower, only got 2 grows to finish and they weren't any good, I bought a HydroGarden tent and its killed about 3 other grows but not using it anymore, and this ones going alright so I could really do with some help!

Growing under 250w CFL, small fan on leaves for air movement, in coco mix witha dash of perlite for good measure. I have given the plants no nutes as the potting mix I used contains enough for 4 weeks.

Will be moving the plants into a 600w growbox at 28 days.

Just repotted my 23 day old alaskan ices, into pure coco mix with no nutes mixed with the remainder of my potting mix about 75/25 to the coco.

5 of my babies have taken really well and are throwing out branches and leaves with no probs but this one has gorn a bit yellow and some of the leaves are burning.

After I repotted I gave them loads of water, didn't water for 5 days until this morning when I fed with organic feed (plagron grow)

Am just wondering why the others were fine and this ones looking a bit sickly, its growth has slowed as well. Am I being a bit over attentive because of all the probs I've had in the past?

looks like nute burn 2 me...if the leaves where yellowed more I would think nit dif but they seem to be brown/burnt

Dude...

Do they even have nutes?

Coco has none :S

Adjust the ph and give them nutes.

If your using organic soil to that coco mix go for 6.5 ph

Check your ph.
where did you get the pots? looks what i need, what gal are they?

pots are 11 litres or about 2 gallons, I got them from a local growshop, I see them in all the grow shops round here. They were about a £1.10 each. it probably is a ph problem since I repotted them cos I've mixed the soil. Like I said I gave them a 1/2 strength feed last time I watered and there would have been some residual nutes left over in what remained of the potting/seeding coco I used initially. I'll have a look into the PH values tomorrow and see what I can do.

Thanks for the replies.

I think the issue probably is PH related since a couple of other leaves have begun exhibiting similar problems, just not to the extent of the one I posted about originally, maybe shes the runt of the litter!

So I had a look into the PH values, I don't know specific values since all I have is the capsules as I mentioned. But the coco mix would appear to be JUST on the acidic side. At any rate I watered again and gave them a full sized dose of the Plagron. I dont' think I should be worrying about it too much as they're otherwise showing aggressive growth, even after topping and the roots are already visible through the stones at the bottom of the pots.

Am going to put them into flowering in 3 days, everything I've read on the net has told me that the strain (alaskan ice) is very prone to going hermie so I hope all the effort hasn't been wasted again!

Heres some pics of them at 25 days.