I've grown DWC for several years and even more harvests. I've never had root problems, I live in a warm climate and if I'm growing in the summer months my water is regularly above 75 degrees. Hell, I've even read 80 degree water a few times and whether it was luck or just being safe, I don't know which it is.. I think the key is to have more than enough movement in the water tanks to keep the water well oxygenated and constantly moving. I use white 48 qt marine coolers for my tanks and I always clean the tanks with Hydrogen Peroxide and water before starting the next batch. I use hydroton pellets and I soak and rinse them several times to get all the crap out of the pellets and I also use a bit of HP when prepping the hydroton. I wipe the netpots with HP and clean everything as well as I can. Another thing is I keep all light out of the water tanks.
My grow is in a walk-in closet with a 4x2x7' tent. I use a 300w LED and a few 68w CFLs around the sides with reflectors when vegging and I add a 400HPS for flowering except in the dead of summer just because I can't keep the grow room below 80 degrees in the summer months with the HPS going.
I've grown feminized seeds mostly and my share of autos. My last batch was Chemdog Autos and the first one was ready 72 days from sprouting and the others ran as much as a month or more longer, pretty easy to get an ounce off the ones that grow longer, the early bird was fast but it only yielded 12g dry. A few years ago I grew some Chemdog feminized from Green House seeds and I grew a 7 footer that yielded 13oz from one plant! That one I vegged for 40 days and then flowered for 14.5 weeks and it was the most potent weed I ever smoked, much less grew... it was so narcotic that at least 4 seasoned smokers got so wasted they got sick. My best batch of autos was some AK49 Autos, I was able to average 3oz per plant and the quality was nearly as good as normal plants.
