MarkS: we have almost the same size pond, a larger deeper pond connected to a shallow smallerpond. I added areation to the larger one which had thick black eggy muck & chocked by mat algae. The areation helps keep the algae in check, a year later I started to use Benificial bacteria to reduce the muck, now you can see stumps with roots in areas where we never knew they were! we also save $ on the chemicals we use to dump in the pond. Now we just treat for weed growth & with the addition of bacteria we cut down on the weed chemicals as well. The key is adding bacteria in spring before the weeds start to bloom. the smaller section had no change it stayed mucky & chocked with algae until I added aeration to it.
