My floating dock just freezes in the pond without issues..so far. I think the big concern is if the ice would tend to shift and rip the dock from it's anchors. My pond is too small for shifting ice.

Augie...I think you'll be fine without keeping the ice open.

Brian...4.5 acres is pretty big. I would think a 4 head would be overkill depending on the size of the dock and can see how you would consider a smaller job specific system. Don't forget that your system is probably sized to run all the diffusers and if you shut half of them off, you will be over-driving the remaining 4. Or, you could dump some of the air to atmosphere to reduce the flow to the operating diffusers.

I have read where some folks used soaker hose as diffusers and a smaller pump for this application, but can't find the thread now.

Fish on!,
Noel