You should switch lighting to high presure sodium. That's the best lights for plants. That's what most illegal crops of weed are grown with.
A 250 or 400 watt
A 250 or 400 watt
You can even ditch the light you have. That particular 'bamboo' only needs glancing sunlight...what you have is likely too much even at 18W.
I added about 15 very mature stocks in an AquaClear 40 flowing at the lowest rate it can go to. In my 90 with a single ray, I have not seen a drop in nitrAte. I would like to double the bamboo amount before I make any decisions one way or the other. I think a faster growing plant that consumes more food through the water would be better at processing nitrates. I'm no hydroponics expert however. Keep us posted of any updates!