I could not wait for an answer. I ended up using "Anti-Vibration Isolation Pads" see
http://www.soundproofing.org/infopag...rationpads.htm . This was used under the bottom of the tank to prevent sound from the floor entering the tank. I purchased the 2" squares and used a hacksaw and cut them into 1" squares. The ribbed neoprene was not glued on very well and some fell off the cork, but I re-glued those with contact cement. Next problem was, now that the squares were only 1", the ribbing on the neoprene was two highs, which did not allow the smaller 1" squares to lay flat. I used the foam insulation product called "Great Stuff" on the ones that were not laying flat to level them out, which allowed them to be glued to the bottom of the tank, without difficulty. I have not finished building my tank, yet. I've completed the enclosure and insulation, but have not placed the fishpond liner into the tank, yet.