Is this Algae? (ID help needed)

[ReefGirl50]

I noticed one of these on my glass a few days ago. Today there are about 20 of these flat discs on the walls of my tank. Does anyone know what they are and what I should do about them?

 

[lil sumpin]

I think that’s green calcareous algae. Eventually you’ll get the purples and pinks. I don’t think you need to be alarmed