Depends what temp you can get your water up to.
Basically all fishtank heaters will get water up to about 30C or so. The wattage of the heater simply affects how quickly this occurs. Overnight my 300W heater (300W is about max for domestic fishtank) got my tank up to 24+, at dinnertime this had cooled to 16+ but I had NO probs re: icing up of hose or pole.
Im getting a 3KW tank heater this week, hoping to get the temp upto about 45-50 once I have that
