I may have missed something here but the OP said he has 3 bottom diffusers, what kind of diffusers? Some types of diffusers aren't very effective and the system may not be matched to his size pond.

My experience with adding bacteria is that it does work in the shallows and it's the only thing you can do to reduce muck if you don't have an aerator. Without an aerator you have to add bacteria at regular intervals, not just once. When I first started adding bacteria (prior to getting an aerator) there was an obvious change in the color of the pond bottom after only one month. My dogs were also much cleaner after swimming. After one entire summer of using bacteria the pond bottom in the shallows looked like it did when it was first dug.

This is my first summer with an aerator and I only added bacteria at start up because I had some left over. It's my understanding that you don't need to add bacteria if you aerate and I believe that to be true. My pond is much clearer now without adding bacteria and I can see more of the (clean) pond bottom.

My unscientific conclusion based on observation is that bacteria alone does work (at least in the shallows) but aeration alone is superior for cleaning the pond bottom

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