What is this algae?

[Daddy-o]

What is this algae growing in my tank? It clumps up and hairy. How do I get rid of it?
90 gal tank
Did a 25gal water change few days ago and it still continues. Got much worse after 7 days without power and had to run tank with just a small pump. Temp got down to 64 at times. Not sure if all that is relevant.

 

[Rutrag]

It looks like hoar algae to me. That's normally from high nitrates or phosphates, and it also seems to thrive in low magnesium environments. What are those parameters, and what's you water source? (Tap, RODI, LFS etc.)

 

[Daddy-o]

I use RODI water. Not sure of parem's yet. What is best way to clean up - have people coming over for thanksgiving and I want to have a nice looking tank!