That looks beautiful!!
I'd love to know what the setting is for your pump!!
How long do you keep it on for?
I have mine on for 15 minutes/every hour/24/7... my lights are 18/6 as well (400 watt HPS)
I've got a single unit waterfarm system with a nice young bushy plant. I have it under a 400 watt HPS light with a large reflector.
The light cycle is 18/6... (and I won't have it any other way; mainly for electricity reasons)
The guys at the hydroponic store told me to leave the pump on...