hi charlie
i think that one reason that leaves curl at the edges a little like yours do is to reduce transpiration-i've had it happen a few times in rooms with v low RH in veg.
they look a bit pale-with no signs of lockout so i guess they are a little hungry. I think that you are under feeding a bit. I put 20ml of Canna A+B into 8L (2gall) when my plants are the size of yours-thats quite a bit more than you are using.
Also-you do need to check and adjust the ph to around 5.8-6.0 in coco-
look into some source of co2 in that room. without ventillation your plants will deplete the co2 in the room VERY quickly, not to mention your plants will be able to rock comfortably at a higher temperature. if you were getting three per plant without co2 last time, all things the same with co2 and larger pots and i don't htink five per is out of the question at all. remember, if you can scratch .7 per watt with those two 400's then you get just over four ounces per plant so your gonna need to be pulling some VERY good yields to get 25 total ounces under that many watts.