Freezing Tank

I have an above ground 1000 gallon water storage tank. I am having a horrible time preventing it from freezing. I've been using a drop light with a 250watt heat bulb inside the tank. The pipes are lined with heat tape and insulated. I've seen the stock tank de-icer's, floating and submersible heaters. Can these also be used for household water tanks? And which type might you recommend? thank you