Hot water as an emergency measure
Leave your garden pond in peace! However, if the surface of the water does ever completely freeze, do not grab your hammer and chisel to hack a hole in the ice. The pressure waves that this causes can disturb your fish and even damage their health. Instead, carefully pour a pan of hot water onto the edge of the pond to create a small, ice-free area – and enable gas exchange. If you want to keep the hole open, you can hang the air stone that goes with the air pump through it.