Penn Plax Cascade Preset Submersible Aquarium Heater, Accurately maintains the desired temperature in your tank. Fully submersible and can be placed horizontally or vertically in your tank. Easy to set and accurate to Fahrenheit.
Aquarium Heater & Passive Solar Heat NOW! (I love these tips/ideas. Simple, frugal and temporary. Warming rocks by candle light, brilliant. Excellent for the apartment dweller during winter power outages.