For 72g with low light, I'd just replace the bulbs in the fixtures you've already got with ones in plant happy color temperatures. Again, one 6500k for maximum plant benefit, and one 10,000k in the fixture furthest forward. Once you have the 2, you can decide for yourself which kind you want to use for the 3rd, depending on how you'd like the color to shift between red & blue.Hmmm...Thanks for the info. I'm doing just low level light plants such as Java Ferns and Anubias. As far as my current setup goes, I have a 2 bulb fixture w/ a Power GLO t5 18000K and a t5 Coralife POWERMAX....not sure of details...but I've had it for almost a year and it's looking quite dim so it may be on it's way out.
I have a 72gal bowfront...