The first step would be identifying the weed causing the problem and most likely followed by physical removal if possible. Secondly, because it's shallow, surface agitator type aerators or horizontal aerators will probably be best. The high oxygen transfer agitators aren't really fountains...forms more of a rolling frothy boil about a foot high but the pretty fountains help, just not as much for the power consumed. Third, you'll probably need to apply a chemical suited for the weed identified.
