in uk we put a tennis ball to float in the pond 1] stops the cement cracking--it expands+contracts-----2]also needs to have some depth

we used to put empty 2 liter and 1/2 & 1 gal milk jugs with the screw on lids into the swimming pools to keep the surface from freezing ( the bottles bobbed and kept the wate rmoving enough it did not freeze solid.

Gosh -- those are good ideas....wish I'd know you all when I had a Koi pond! This has brought back a funny with ours. DH went out that morning to break the ice. Do you know what ice sounds like when it's being broke up at 6:00 in the morning??????? Our neighbor told us later that he called the police because he heard glass breaking and thought somebody was breaking into houses or cars!!!! whoops!!!! LOL

we have 2 levels in our koi pond...the fish stay in the lower level in the winter. It doesn't freeze and they were just fine last winter...and the pond was frozen. we turned off the pump in the middle of Nov. and they would still come to the surface for food, if they saw us. Didn't loose any last year, but lost 1 the year before.

They should be fine...

It really does sound like glass breaking.
That is so funny!

Check out koiphen.com Everything you need to know about koi/goldies is there.

Also, never break ice up-the sound is too much on their system. Pour hot water over an area til it breaks up.

Depending on the size of your pond and fish and how many fish you have, you do need to let some of the gas escape.