Single diffuser would work, if you don't push the limit on biomass, but since it is an older pond it all depends on the amount of organic build-up you have. I would plan on running 2 different diffusers/stones to play it safe. Air stones will create larger bubbles for more "wave" action. 1/4-1/3 hp compressor, put whatever you use to make bubbles at 4' water depth. I don't like using stones for summer use, as I believe they make larger bubbles and don't move as much water as rubber membrane diffusers. I would still place them close enough to shore so that anything that goes into the cold pond water can walk out of the pond.

You won't have problems with ice and the pier. The family has had a fixed pier on a lake (S-SW corner) since the late '60's without any protection from ice and never had a problem.

It all depends on how much of a gambler you are. Save money and use one, maybe pay what you saved to replace fish that die?

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).