Do Actinic bulbs need replacing??????

Hello all.

Long time no post. I hope everyone is well. Summer kept me busy with other stuff. Now that we're headed for winter in the midwest I'm back to my aquarium. It has actually done quite well over the summer.

Anyway I'm getting to the point where I should replace the bulbs in my power compact fixture. It has (2) 65 watt full spectrum and (2) 65 watt actinic.

Do I need to replace all bulbs or only the two full spectrum? I ask because most everything I read indicates actinic are only used for aestetic reasons - to balance the full spectrum and make everything look more pleasing and true to color. Many articles go so far as to say they have no impact, positive or negative on coral health.

If this is the case why would I care if the actinic spectrum shifts as long as the aquarium looks nice? It could save me a lot of $$$$$$$$.

Another related riddle - my (4) bulbs give me 260 watts of total light - or a little less than 5 watts per gallon in my 55. If the actinic lights don't impact coral growth - do I only have 130 watts of useable light?

The actinics keep more of the light shifted toward the blue spectrium.Which is the spectrium that the corals need.As they become burned out,they loose spectrium which means they shift more toward red,which algae uses.Of course thats just my thoughts on it.
But I think you need to replace both.

With pc bulbs, you should replace them all every 6-8 months. As Yote said, the actinics provide the needed additional blue spectrum of light that the full spectrum alone don't provide.
Actinics can be replaced less often when they are only used as supplemental lighting like in a metal halide setup where the mh bulb can provide all the needed light.

I've read, more than once, that the blue actinics stimulate red and pink coralline algae growth.