Emo, did you check your water parameters recently? Ammonia, nitrites, nitrates, pH?
Just because the water is green, and you can't see your fish, doesn't mean the water isn't healthy. I have a totally green pond with comets in it, and I can't see my fish for the life of me. Its actually much better for them - predators can't see them (duh!
), the green water brings out much brighter colors as well.
How many hours a day does the sun reach the pond? A pond sitting in full sun all day will get green eventually, there is no way around it. Some shading above the pond will help, but ultimately I only found the UV sterilizers to really be effective. But remember, I live in Florida, so sun wise there is a big difference to you in MI.
High nitrates or pond waste, like plant debris from trees, also can atribute to the green soup.
I would try a bigger water change and get some shading over the ponds for starters. There is also a product called "barley straw", that you can add into the pond, and it supposedly helps with the green water. I have never used that though, and I am pretty sure it will lose its effectiveness after a while....
