Red algae

[daplatapus]

Maybe fill us in on your system and we can help out a bit better.
How old is your tank?
How old are you bulbs?
What's your lighting schedule?
WHat is your feeding schedule?
What's you livestock?
What's your flow in the tank?
What are you tank parameters? Nitrate, ammonia, phosphate?

Stuff like this is almost always related to nutrients and flow. Finding out where the nutrients are coming from and what the bacteria is eating will go a long way in getting rid of the problem.
I've never had it, but I've heard 3 days of a blacked out tank helps, but unless you get rid of the nutrients it may just come back.