You should have alot more growth in the newbies at day 31. I would have to speculate at this point there is a common denominator to this problem. As in the lighting, humidity, soil, something. The bigger plants are looking about 7 days old give or take. Im amazed to say the least.
Let me re-read some of your info and take another look at those plants before I say anything else.
Ill get back to this in just a sec...
Alright Im back.
So I would suggest finding yourself a low dose of starting nutrient. Miracle grow sells one, so does shultz and other Nute companies. Something like this would be just fine:
http://www.amazon.com/Miracle-Gro-100556-48-Ounce-Quick-Liquid/dp/B000RNB3BU
And once you get it set it aside. When you need it premix a gallon in a seperate jug at 1/4th strength. MJ burns easy, so always use 1/4-1/2 strength if you are using regular non mj nutes.
Anyways, a good stimulater would help, but lets just try the tap water and better lights for now.
People will talk poorly about using nutes that arent specific to MJ, but really do you think people had MJ nutes in the 70's?
MJ specific Nutes weren't popular untill recently, and until then people understood that organic matters and compost were the variables and chemicals where easy. Nowadays people overthink the additives, and dont let the plant do its thing the natural way. Atleast that seems to be more common.
Anyhow, to fix your plants I stand by my original diagnosis.
If 3 days pass and shit hasnt started happening, try a growth stimulator geared towards transplanting plants. As long as its for transplanting, its a stimulator.
Use 1/4 strength of what it says on the bottle, never add directly to the plant and you will be fine!
Im sure we will be talking more when you swap to the flowering room, 600w lights are no joke. If you are having problems now, you should really start studying because shit gets alot harder in the near future.
OH YEAH, next time use scotts soil. Even 7ph, advertised on the bag. Good stuff, has all the right elements to get your goods growin, cost effective too. Then let your plants tell you what they need. Dont go adding shit for no reason, feed them regularly and if they need something specific learn to diagnose that.
Greg Greene makes a great cannabis bible, and V2 is even better.
Id check that out, chapter 13 has a great problem solver section....
The only other thing that would make sense IF I am wrong is that your pots/cups arent draining correctly, and you are in fact overwatering. You seem pretty positive thats not happening, so lets not think thats whats going on.
TO WATER: stab pinky 1-1 1/2 inch in the soil, if finger is dry water. If not, or even moist in the least then dont.
Good luck hippy!