TPG, are you still feeding pellets? If I were you I would stop or at least significantly reduce the quantity.
I don't know much about maintaining fish in ponds but I've had my share of aquariums. I also worked in the local pet store when I was young and the owner was an ichthyologist. He always stressed to people that the primary reason for bad water quality was overfeeding. He said that with aquarium fish you could stop feeding and the fish wouldn't starve for quite a long time. In a pond I think it's accepted that you don't NEED to feed at all, and I'm sure that I wouldn't be if I was in your shoes.
Please don't act on my advise without hearing from someone with more practical knowledge though.
Good luck and welcome to the forum.
