How high above the substrate do you plan on having the light for medium or high light?
not quite sure yet, I will take a PAR meter to it when I get to that point. the tank itself is 18" with ~3" substrate, 15" to the top of the tank. If I use the same distance my current 36g is at it would be a close bet I will have high medium / high light at the substrate. I will probably back off a little bit from there since you can really grow most plants at medium light.