I wonder if someone can help settle a debate I am having over using air compressors to aerate garden koi ponds? A typical pond will have a small electric air pump (44W rated, delivers say 50 litres a minute at 1.5 metres deep in a 10000L pond) blowing air through a diffuser to add oxygen and create movement in the water. The air leaving the pump is of course hot once it is compressed, my friend is convinced this heat is transferred to the pond, I say no it will all be lost when the air returns to the atmosphere at normal pressure. Also where does the 44W input end up? Since the debate started the subject of evaporation has occurred and what effect this may have on the water temperature particularly in winter when air temperatures will be lower than the water in the pond so any thoughts on the significance of this would be great.