Andy, what caused the green water?
Or is that algae on the glass?
Yes. To both.
Phyto "spores" (I don't know if that's the right word) are everywhere, carried in the winds. They just need someplace with the right requirements to get 'em going. I would assume that the phyto came in on my sand, along with whatever hair algae that grew out so quickly. I've never seen hair algae like this. It sends out crazy long strands (at least two feet long) and immediately sprang right out of the sandbed, so I know that's where that came from.
But, like everything else around this hobby: Wait it out, do what you can. I don't have enough filter feeders to control the microalgae yet, nor enough herbivores to eat the long stuff. Fortunately, conchs and hermits seem to love the long algae, so I have some of them working on it. I've also gotten what I have left of my DIBS snails working on it. I hope that they have a population explosion coming soon. I should have some more DIBS creatures coming next week. I added some gracillaria, ulva, and chaeto to try to out-compete the hair, but the copepods wiped out my ulva.
And, I added a tomini tang to the frag tank tonight to try to keep the corals clear. The purples aren't too impressed with the hair algae, unfortunately.
So, wait it out. If I was smart, I would have waited to add livestock 'til this all died back. Now, feeding the fish is feeding the algae. Bummer.
On the other hand, I don't particularly care if algae grows in the basement, so long as it doesn't kill the corals in the frag tank. It's taking up nutrients, which is what those tanks down there are for. Otherwise, it's all zooplankton food.