Soft green algae is generally considered good if you have herbivour fish. This is esp. true in ponds, where those algae linning the pond don't obscure the view of the fish as in an aquarium. I clean only 3 sides of my tank & leave the back for algae (and the goldies generally keep those closely cropped).
Others are OK if under control - eg thread, staghorn.
The Baddies are those that take over your tank & are impossible to get rid of - eg. BBA, green water, & BGA (toxic).
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.