What is this, a plant for ants? (Midget growth) Help Required

Hi,
This is my 2nd post. Bare with me. I'll try and post as much info as I can.

I'm doing this as a 'test phase' to understand growing better, before I buy some expensive seeds. I don't want to spend / waste time & $ where it's not needed + we don't really have a lot of $ to begin with.

Seeds: Unknown strain and sex. Found in stash.
Grower: First time
How: Hydroponics & Hand-watered
Current light: 600w HPS
Veg Light time: 16/8
Room temp: 27c - 29c with lights on
Air cooler: Yes, just got a 2nd hand one as of 21st Oct 12. Hopefully it'll help with temps.
Exhaust & Inlet: 2 x 4" fans.
Space: 3ft (width) x 2ft (depth) x 4ft (height)
Ph: 5.5
PPM: NO IDEA, Waiting on meter.
Nutrients: Yes. 1ml/1ltr
Age of plant as of 22nd Oct 12: 9weeks

I initially started these plants under 2 x 150W CFL's, before I gathered funds for the 600W HPS. (The CFL's were 5,500k not 6,500k, so not ideal to begin with).
The growth was good under the CFL's, a bit of stretching which I gathered was due to the lack of light. They spent 5 weeks under those lights. Nice big leafs.

4 weeks ago, we switched to 1 x 600w HPS. The plant suffered a bit of shock and a few leaves turned yellow and a few edges got burnt. You can see the pic of the one closest to you. So I've raised the light up and haven't had any burning probs since then.

I've noticed the leafs are much smaller now and the plant isn't as stretched. I understand the reduction in stretch, but the leaves being so small, I have no idea.

I've topped both plants (two times each I think) about 2-3 weeks ago but that was it.

I'm going to put them into flower soon, so I can identify the sex.

For the moment, I'd like help on why the leaves have nearly halved in size.

Thank you, Cheers - XYZ

It is getting older,and showing Sativa leaning expressions would be my assumption.
You did do a shocking,instead of easing in the HPS over time.
You should learn cloning,and sex the clones.
Get a 30X loupe,and look for preflowers.

whats you water ph u have some serious probs i wouldent even think about flowering till there healthy

did you transplant them when you switched lights? maybe youve damaged the roots? or maybe your pots are too small and theyre rootbound?

also you say youve topped each one twice.....topping can reduce growth by 2 weeks as the plant needs to heal.

depending on strain you may be ok... my buddy had a purple haze from g13 that was flowering for 8 weeks and never got higher than 3cm tall...he put in flower just to see what happened..... and it grew to about a foot and plumped out 2oz dry.... he showed me in amazement and all i can say is it looked like a 1foot bud growin out of soil!! it was pretty impressive!!

i kno its a long shot, but the pics look like some cuttings of pure ak that ive seen around, the original was a bush...but the cuttings grew just like in your pic...they each pumped out about 2oz each. pure ak is a great strain. if thats what yours are you wont be upset, but like i say...theres a million strains that look the same!

bonsai ...........

I didn't gradually get them used to the 600w. The ph is 5.5.
The pot isn't small, it's 200mm x 130mm. (7in / 5in approx)
I've got a 45x microscope to check for their sex, no signs yet.