Posted: 10/05/2013 at 19:19
I have just been listening to a previous edition of Gardener's Question Time all about this. The problem with thick ice forming is that noxious gases are trapped and the frogs die because of that. The best way to prevent this is to float a tennis ball or football/beach ball depending on the size of the pond to prevent the ice from completely closing over, and to check it daily. Apparently cracking the ice after it has frozen can cause deadly vibrations to overwintering frogs, so the ice should be kept clear from the outset, where possible, and never use salt, boiling water or chemicals to clear it (apparently some have resorted to these ideas). Also, be sure to include lots of oxygenating plants such as hornwort, to help keep oxygen levels up and provide cover. When snow falls on top of ice, clear the snow off, to allow these oxygenators to carry on photosynthesising. Also, you could line even the bath and that would help to insulate. It is apparently not so much the depth of water, but the lack of air circulation that causes most deaths.