I'm a little late in this discussion, but my opinion is only to replace actinic lights when they burn out - that may be 6 months or 5 years. The reason is that actinic lights are only there for your benefit, not the corals'; no significant increase in PAR is added, and no additional photosynthesis will occur from the blue range of the spectrum. Use a PAR meter if you don't believe me.
We replace bulbs on aquaria because there are slight color shifts over time, and the corals will get less and less available light for photosynthesis. Since actinics aren't adding to that, there's no reason to change them out until they burn out or you don't like the look anymore - the corals won't know the difference or grow any better / worse, and you'll just be throwing away good bulbs.
As for the HQI, I'd replace it every 6-9 months. HQI bulbs run hotter than SE bulbs, and thus will see the end of their useful life faster. Of course, the best way to tell is to measure your PAR, and when you've lost a certain amount (say 10-15%), replace the bulb.
We replace bulbs on aquaria because there are slight color shifts over time, and the corals will get less and less available light for photosynthesis. Since actinics aren't adding to that, there's no reason to change them out until they burn out or you don't like the look anymore - the corals won't know the difference or grow any better / worse, and you'll just be throwing away good bulbs.
As for the HQI, I'd replace it every 6-9 months. HQI bulbs run hotter than SE bulbs, and thus will see the end of their useful life faster. Of course, the best way to tell is to measure your PAR, and when you've lost a certain amount (say 10-15%), replace the bulb.
