ARRGHHH. So I've spent about two and a half hours typing this thing up and waiting for pictures to upload, and upon reading midgrade's response, realized that the last part that I had just posted for some reason never showed up. Tja. So I will give a quick response to midgrade, as I have left out some of the things he questions, and post the last set of pics that are from yesterday.
Containers: The containers are probably at least 1.5 gallons. I learned that same rule from Jorge Cervantes on the grow DVD, and took it to heart. Plenty of room for roots, plenty of porous material mixed in to facilitate good drainage and oxygen delivery to the roots.
Stretching now, and I think you can see it in the pictures, is no longer really a problem. Under the HPS, it seems to be coming in dense and bushy anyway, and the plantastar 400W with the extra blue spectrum seems to be doing its job. That really doesn't seem to be a concern, but maybe you disagree...
Ferts were unfortunately in my last post:
I decided that I would not be buying some expensive marijuana-specific fertilizer, as I have spent enough on the grow up to this point and will have a hard time convincing my wife, who doesn't smoke, to shell out even more money on this project (even though she will be ingesting some buttered deliciousness on occasion...)
Inspecting the nutes we already have at home, I came across some cactus fertilizer and bonsai fertilizer, and seeing as both had higher 2nd and 3rd NPK digits, decided to mix them. The cactus was 3-7-5 and the bonsai was 3-5-7 or vice-versa, leaving a solution (if balanced) of 6-12-12, a combination I have seen said to be appropriate. I have been using a 1.5 L water bottle for nutrient and water purposes, but the dilution instructions were different for each and required a little calculating to balance them out somewhat well. The final concentration works out to 13.5-26.3-28.3, which seems more on par with what I've seen.
@Mitgrade: I had been using 7-6-3 ferts during vegging stage, and had noticed how small those numbers were compared to other fertilizers, and have noticed no ill effects from the "double dosing." Could your rule have something to do with fertilizers of a higher concentration?
Watering, although tempting to do often (and apparently due to its ability to lower the temperature somewhat in my closet) has been done in my opinion correctly. I watered them today with the bonsai/cactus solution, .75 L per plant, and no water came out the bottom after I was done. I had not watered in 4 days, and had patiently waited until the middle of the soil had dried up before going ahead and watering...
Ventilation is no longer a problem: I have an inline fan set to clear out 410 cubic meters/hour. 410/12 will give me the amount cleared in five minutes, and this is over 3 times my grow area of close to 1.2 cubic meters. There is also a little fan hanging from the ballast, blowing the heat towards the coal filter to be jetted out quick, and this seems to be keeping the temp. around 28 degrees Celcius, but I can't go any lower than this when the temp in my place itself is also that high. No A/C in europe makes growing in summer a challenge, to be sure...
Thanks for the comments, and I will keep pictures coming every couple days. Let me know if something seems really out of place...