Green spot algae, also known as green coat algae, is found in every aquarium. These green algae (chlorophyta), which cover glass and structures, are relatively easy to clean because we have the most weapons to combat them, including: algae scrubbers, and algae-eating catfish and invertebrates. As green algae, they do not cling tenaciously to surfaces like the red algae do and thus can be cleaned relatively easily.
Green pot algae is normal fauna of the aquarium and doesn’t typically cause a huge problem. If it starts being a big problem, look at the phosphorus and nitrate levels. Green spot algae will grow slowly with virtually no nutrients so the only way to keep it out of an aquarium completely is by leaving the lights off.
Here is a link to an article on controlling all types of algae, including green spot algae: