help with replacing lights

[pteam]

Hey guys quick question. I have a 150 gallon reef tank (6 feet long, 2 feet high, 1.5 feet wide) with some soft and hard corals, a clam, and lots of fish with 3 250watt metal halides (I think theyre 15k) that come on for 6 hours a day and 4 54 watt blue looking t5 lights (bulb says "Ch Lighting F54T5/Blue-Lux Coral - all 4 are the same) about 45 and 3/4 inches each that come on for 13 hours per day. Most of the corals are midlevel to higher level in the tank as theyre almost all on live rock. Everything has been doing real well for over a year, however I've had all the lights in there for a year and I think I should slowly start changing them. I was thinking about changing the middle metal halide and then a month later changing the 2 side ones. Also there are 2 blue t5s on each side 4 total. I would like to change out one on each side, then wait a month then do another one on each side. However wouldnt it be better to have two different color bulbs on each side? Like on each side have one that is blueish and one more purplish for a better spectrum? Recommendations?