Wow that's some crazy algae growth! Does their tank get direct sunlight? I only seem to get the brown slime stuff in my tanks, but I keep them dimly lit
I wonder if I can cultivate some green algae in a container outside without attracting the most-quit-toes. I can picture spending my mornings scraping algae out of plastic containers to feed to the goldies

It should have the affect of keeping the goldies in green water, without actually keeping them in green water?