Tom,

How much submergent vegatation do you have? Have the grass carp eaten it all or is it scare? If your macro submergant plants are scare, or nonexistant, your FA is taking up all the nutrients coming into your pond which of cours cause it to proliferate. Too many amur could actually be aggravating your algae problem by eating too many of your submergent macros, and due to a very short digestive tract quickly converting them into nutrients in your pond which aggravates your FA.

Case in point. I have nutrient rich trout pond due to lots of feeding. I have three plant organism that uptake nutrients:

1.) Chara (Skunk weed) acutally a large form of algae that looks like a plant.

2.) Phytoplankton (suspended algae that colors the water green)

and

3.) Filamentous algae.

I have found if I rake out a lot of the Chara I get a proliferation of FA. That's because something uses the nutrients and if the Chara is substantially gone the filamentous algae takes over.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.