i know this doesnt really answer your question but i'd like to add, supplementing oxygen to roots is very underrated in hydro. you say you have an air stone, and that is pretty much needed. is it a pretty decent one? i prefer air diffusers myself. they make ones that fix exactly in a 5 gal. on my deep water i use
http://www.ebay.com/itm/Oxygen-Shield-Air-Diffuser-OS5-airstone-hydroponics-aquarium-water-pump-/200696838185?pt=LH_DefaultDomain_0&hash=item2eba76b829 with this you also need a pretty good pump. i use one somewhat similar to this
http://www.ebay.com/itm/Air-Pump-Sunleaves-DuraPump-1030-gph-for-Hydroponics-Aquariums-Aeroponics-/350491823631?pt=LH_DefaultDomain_0&hash=item519af0ce0f it's insane all the bubbles it makes.
if your air stone is pretty good, you should be able to get away with it just fine. i've used cheap ones for aquariums before without much trouble. get a good pump and a diffuser and it's a really nice boost for you plant's health.
as far as that t12 light, they are not really that great for growing. you may be able to veg under it ok though. most ppl just use t12 for cloning. t5s have a much better output and are not all that expensive. keep that light as close as possible but dont let it touch the plant. a 26w CFL with a decent hood, all which you can buy at walmart for pretty cheap, may actually be even a better light setup for a plant that size. or you can get several around it. the cheap walmart hoods even have clips so the placement of them has a lot of versatility.
if you plan on getting that plant big and want better results, i would get a hps. even just a 400w isnt too bad. just make sure to try and keep that water cool. 68F is best. you can get away with warmer water temps but you will probably get root rot. you can still have a great crop, but you yield will suffer. i've had my water temps as high as 80F and still got about 5 ounces a plant. it was grown pretty big and had excellent lighting though. dont confuse that with your room's temp. that you want a bit warmer like 75-80F. too cold and you risk powdery mildew. humidity is the biggest factor for mold, but from my experience, temp is another real big thing. some strains of PM dont need much humidity. just the little condensation from the temp changed caused by going from light to dark is enough for spores to reproduce. read this is a gardening magazine and found it to be very true.
good luck
