I don't quite have the answer for you, however, are the light T5NO or T5HO? There's a huge difference between the two, especially since your tank is pretty deep. If they ARE T5HO, then make sure to get pressurized CO2, or at least DIY CO2, or you'll be seeing an algae problem pretty soon. If you have mounting legs, you could use those and just not use the acrylic top as it may be a bit more aesthetically pleasing for you, I know it is for me personally. However, as long as you keep the acrylic top clean, I don't see a problem with the acrylic top in terms of light potency.