was interested in this topic as well as ive just switched to a 6 bulb fixture and was curious about bulb changing. When i got the fixture, the bulbs were probably 1-2+ yrs old judging by the "burnt" look near the prongs...
So I just changed them all out....at once... no problems. Had an algae bloom but that was from NitraGuard BioCube thingys. my bad....again.