Alright, I've Been Thinking...

[FishBlast]

When life gives you lemons... Wouldn't it be cool to have a background covered in green algae? But... how does one acquire green algae? I can't even grow any type of algae here anyway (the reason why I have to feed my apple snails manually).
Does green algae require a higher light wattage? Or can it be acquired somehow from somewhere? Are those moss balls made of that algae?