Black algae in saltwater storage tank

[Heart of Dixie]

A few months ago I bought a bucket of Coralife salt after using IO for many years. Today I looked in my saltwater storage tank and there is a thin layer of black algae where the water touches the sides and bottom. I checked the RO tank and it is clean. Both tanks are opaque. I never had the problem before the salt change. Has anyone else experienced this? Thanks for any input.

 

[lapin]

Are you sure its algae? Is it film like and slimey?
My mixing barrel has a slight tint to it after 2 years. Its not algae, just some build upchemical residue.

 

[Heart of Dixie]

Yeah, thin, black, film like and slimy.