on my tank now i'm running 2-250 10k and 1-400 20k. i really like the mix. i'm also running 4- 4' VHO 2-white and 2-blue. on the tank that i am now setting up i will have 3-400 and 2- 72'' VHO blue and hope thats enough. tank is 84''long x 36'' wide x 26'' tall. 340 gal.