If you don't want to drain/excavate, use aeration and bacteria. I am in a similar situation and the muck level is reducing, I just noticed today, my dogs are no longer coming out black and stinky when they get in the pond, I'm coming up on 2 years of owning this place and working on the pond, I would say I've lost at least 2 feet of muck probably more in spots. As far as which bacteria, this is anyone's guess, they all make the claim of some amount of inches per year but have not seen any hard data on bacteria use.
