Lonewolfblue
Aquarium Advice Addict
As I was going through some sites on algaes, I came across this. Here's what they say about the green spots that are hard to remove from your glass....
http://www.aquariumpros.com/faqpro/algae_1.shtml#05200260
http://www.aquariumpros.com/faqpro/algae_1.shtml#05200260
There are also very hard-to-remove little dots of green that sometimes grow on aquarium panels which also are not algae, but diatom or radiolarian colonies (microscopic, one-celled, animals with hard shells) with algae incorporated in their matrix.