still problems - advice needed

these plants were germinated 6 weeks ago and have now been under the 18/6 600w hps for 4 weeks. since then they have also been receiving a good dose of nutrients.

per 10L:

coco a - 30ml
coco b - 30ml
rhizotonic - 20 - 30ml
cannazym - 20 - 30ml (last two weeks)

http://www.canna-uk.com/additives

i messed up the ph levels at first but now i've been keeping it at 5.8. it seemed to improve the overall look of the plants but i still feel that the growth is slow and the leaves look light green. the one on the last picture hasn't grown at all during the time under 600w and the other experience damage as soon as the leaves reach certain size.

any idea what could be going on with my plants and why are they under stress?

does anyone have any experience with such products:

http://www.u-gro.info/

thanks guys!

nute burn, maybe heat stress

take it easy with the nutrients my friend, at this age they could still only need a half or a quarter dose

how close is the 600w to the plants? what are your temps?

thanks for your thoughts mate. i'll keep the nute levels lower for a while and see what happens.

the temp is around 25C and the lamp is quite high up.

so now i've been watering less and they seem to be greener and growing a bit better but as you can see from the pictures when the leaves reach this size they start turning yellow and eventually they die. also the new growth is suffering.

i have humidity problems also...i'm not really able to get the humidity go above 40% i have a humidifier in the room also but as soon as the lamp turns on the humidity is gone. temp is around 24C.

any ideas guys what i should do? these plants have been under 600w for over 5 weeks now and the growth has been slow as you can see. i'm getting a bit desperate now

pls anyone?