Blue/green is cyanobacteria
Algae-eating fish - Common algae eaters such as plecostomus, otocinclus, and grazers such as goldfish or gouramis will not touch the stuff. Why? It isn't really algae. Blue-green algae is a cyanobacteria that is exceptionally difficult to get rid of once it takes hold but definitely doesn't taste like the "real algaes", or actual plant algae.
While it's difficult to get rid of the algae altogether close attention to the tank's maintenance can limit the algae and keep it from reaching harmful levels in your system.