I used to use vacuums a lot and also once made them for sale. I don't any more. Here's my page on pond vacuums.

But if the pond bottom is clean I don't see why a vacuum would help. Google "pond foam fractionator" and/or "pond protein skimmer". Easy to make and effective. I integrate a fractiontor into the pond by making a catch basin for the waterfall. Foam collects there and never on the pond surface.