Leaves yellowing in different ways, any help?

Im into week 6 of veg now and I have a few problems that have been getting worse for the past few days.

The lower smaller leaves are slowing starting to yellow from the tips in. The same things has happened to some of the fan leaves further up the plant. It seems to effect the leaves that grow in pairs towards the base of branchesworse and earlier than others, but leaves further out the branches are getting yellow tips now aswell.
One lower leaf on one plant got a hole aswell, just on one leaf. It's not growing any bigger now.

The top leaves are starting to turn yellow now as well, but mostly between the veins.

I have the plants under a 600W hps lamp, started feeding 1/4 nute dose every second watering about a\week ago (N:K 8:2:6) , the prolem started before this and hasn't getten any better or gotten worse faster since then.
I have them in some indoor potting soil, not great quality and I think that might be the root of a lot of the problems I'm having. Can I repot them into a bigger pot with a higher quality soil at this stage?
Watered today with water pH 7.4 (I know this is a bit high, it's usually lower) and the run-off came out 6.6.

Any ideas or suggestions? Hoping to put these ladies into flowering in 2 or 3 weeks and want to have them healthy from the start if I can

i think your experiencing an iron deficiency.. along with a magnesium def.
Check out these pictures

http://images.google.com/images?client=safari&rls=en&q=plant magnesium deficiency&oe=UTF-8&um=1&ie=UTF-8&sa=N&hl=en&tab=wi

http://images.google.com/images?client=safari&rls=en&q=plant iron deficiency&oe=UTF-8&um=1&ie=UTF-8&sa=N&hl=en&tab=wi


I do think that as soon as your plant has filled up the space in the pot with enough roots.. u should buy some high quality ganja potting soil Order it online if you have to.. but it surely prevents alot of problems you would come across...`

Now if your ph is off, you could be locking out certain nutes like iron and mag... and Nitrogen.. etc.....

try and use some mollasses 1 tbsp per gallon of water... or maybe a bit more in this case.. it should give it the iron and mag your plants need

I hope im right on this one... but doing a little research more wont hurt...

Im putting my bets on mag and iron... its for sure not zinc or calcium, its not phosphorus or pottasium... Very slight chance it would be Nitrogen cause your giving it an N of 8... which is enuff..=)

Goooood luck my friend
keep me posted

Thanks jahtrip, your a life saver. I'll give it a go in their watering today and let you know how they get on.
I owe you one, again

I have a problem as well on one of my plants the leaves are yellow from middle of plant and then when u get out towards the ends they get real green to the tips and look like soggy ish.....Imma try to get a pic and post here, but untill then any suggestions? Thx

Ok this is my first pic uploading here hope it works....the leaves are not as yellow as the pic makes it looks just a faded green from middle n towards tips get greener and looks a little water logged on the ends, what is this from?