That looks like a really healthy root system. Great picture too. Do you use a dome? For the light I was looking at a HLG 65w; is that overkill? If so what t5 fixture would you recommend? Mind you that funds aren't a concern as much as quality, performance and appearance.
I have my cloner in a 2x3x3' tent. I keep the reservoir temperature at 78F using a 50W fish tank heater. I keep the ambient air temperature in the tent lower than the reservoir temperature (68F). I use a 23W CFL for light, hanging not above the cloner, but off to the side. All three of these tactics force root growth and prevent leaf growth which greatly reduces or eliminates the discolouration of the leaves because if the foliage isn't growing, the plant isn't using the nutrients stored in the leaves.
See how the light is more beside the cloner than above it (the pots in the pictures is where I usually start seeds. In this case, I'm starting basil):
As far as a dome, I don't normally use one, but see those screws with the clear tape around the rim of the cloner? In the summer, my humidity goes way down, so that tape is there so that I can lay a piece of clear vapour barrier plastic on top to keep humidity in and the plastic won't touch the plants.
