Welcome Alex. This time of the year there is a LOT of pollen being blown around from the trees - more than usual. I have the same thing on my pond, and this year is worse than previous years.

The muck is most likely a build-up of leaves in the pond (amongst other things). Aeration will help if the aeration is done in the deepest portion of the pond (for the warmer months - move the diffusers to approx. 1/2 max depth for the winter). Tilapia might help too if stocked at a high density.

The pond looks great. Are you dodging many little green piles from the geese?

Lets see what some of the resident experts have to say.

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).