Fyfer,
You have already gotten advice from experts far more knowledgeable than I, but no one has talked about the strength and direction of your prevailing winds.
Is your aerator location "upwind" from the bulk of your pond? Water ice can sometimes have strange crystallization manifestations. Is there a chance that you are making a little bit of slush with entrained air bubbles at the aerator and the wind is pushing it around the rest of the pond? That could be preventing the formation of your solid "skating" ice.
You might be able to change the location of your aerator, with the result being DO for your trout AND solid ice for human recreation.
