Advice welcomed - 1st time under HPS

Hi Guys, and thanks to those who help make up these informative message boards ;)
I've been growing indoors under 2 4x48" 40w flourescent lights (Skunk No1 from Sensi Seeds, in lightly packed compost) with great success - I've always been amazed at the amount of buds/trichomes you can get in these conditions!
I recently purchased a 400w HPS with the idea of using this for flowering and the flouros for vegging/mother plant. However, so far, I'm not enjoying quite the success with HPS and I'm beginning to think it's far easier to stick with flouros (not that I will of course)! I attach a pic of the room the HPS light is in (I usually close it off with mirrored warddrobe door, unless it's getting too hot) and my main problem is heat and humidity (or lack of thereof!). It's currently around 30oC and 25% humidity which I know isn't suitable enough, however, I really don't want to seal the unit properly and fit extractors etc., so I'm happy enough letting them cope for the time being, although I'll buy a humidifier and another desk fan soon (I'll use one fan inside to blow air out and another outside to blow air in).
I attach some pics of my latest attempt (4 females out of 4 from seed - nice!). I vegged for about 4/5 weeks (10 or 11 nodes I think they had) under flouros and transferred them to HPS about 8 days ago when they were about 12-14 inches tall (the last plant I put under there was really healthy until it got too hot being 1ft away from the bulb. I had to chop that one earlier than I wanted so I've kept 'em short this time!). They're looking pretty good and I've given them some 5-5-6.5 fish/bonemeal fert (during veg gave them Sulphate of Ammonia - 21% N), but I think from what I've read that they could be doing better (apart from the really obvious things like hydroponics)! The lower fan leaves are beginning to gradually yellow which a lot of people say is part of the flowering process. However, I've seen fully flowered plants looking totally healthy, so I believe I am lacking something. Is it N, or does it need more flowering nutrients? Or is it something else or nothing at all? I thought it could be a fert deficiency when I noticed the new growth (see other pics) didn't look that green. I know new growth is lighter at first but I noticed this seemed particularly notable compared to other occassions.
So, I obviously need a better growing medium and an easy (please) way to optimise the climate. Where I really need guidance is on the nutrients (BTW the ph is c.7 so could be lowered a bit as well). Apart from the very lowest fan leaves, the rest of the leaves show no sign of nutrient burn so far and I'd like to keep it that way!!!
Thanks in advance for any advice and I'll be sure to update you with any advances! Cheers, Rich

If anyone fancies replying to this, or can even diagnose the problem I'd be very grateful as the problem is getting worse! See my post under "Plant problems" for further info!

They seem great to me.Yah I did one plant under florecent light didnt like it,I just had to keep buying lights.But with 400 watt jeez dosent need more light it already has enough light.But im a newb so don't take my advice totally.don't need florecent light I think.venliting it sucks balls.Have to do more shit wire up more shit and so on.Me im gonna do a new grow in a month planning on growing White Widow.anyways they look good to me.Also im gonna do HPS but very cheap like 20 bucks :D.I notice no one has replyed yet except me is maybe cuz he wrote your thing to long.put into paragraphs your eyes wonder off you know what i mean.When I was reading it I did that alot.Your not alone I did it alot too wrote crap load then no one replied cuz it was too long.just suggesting something.