My fixture is 72" hamilton cebu 3x 400w Mh an 4x 80w T5. The tank is standard 24" deep 180 gallon. I currently have the lights 6" above the tank. Should I go higher??
I would say get them up about 10-12 inches. With 3 400w MH and T5 you have more than enough light. I used 250w MH over my 24" deep tank and grew everything with no problems.