I had alot of "negitive space" out the top of the 40 gallon tall... you can only stack the live rock so high when the tank is only 12" deep... and I've been wanting to upgrade my lighting for a while now because of the depth and to see my corals really start to thrive. Now, by downgrading, I have the light alot closer to the corals, the tank rock work is fuller looking, and the Watts per gallon is better (130W PC to 29 gallons).. also the stand and canopy still fits perfectly!