On my 135 (6' long) i have 2-400 w MH with reflectors the full lenght. It works very well. No need for 3 MH IMO. If u have a center brace then i definatly wouldnt get 3 MH, it will probably melt the pastic. Actinic is nice. Before u do anything make sure u have 2 seperate breakers for this...