Suitable for 3-5 Gallon Aquarium: Submersible Betta Aquarium Heater is the perfect way to ensure the temperature in your fish water aquarium is at an optimal level for the comfort and well-being of your fish. your pets. Ideal for 3 to 5 gallon capacity aquariums, these 25 watt aquarium heaters are a great way to keep your fish happy, healthy and alive. The way to measure the heater in watts for your aquarium requires: Watt = (tank length * width * water height) / 1000 * 2. Durable and unbreakable construction: made of high-grade plastic resistance, sandy quartz filling and high quality alumina ceramic heating system, its durable construction is shatterproof, waterproof and explosion-proof. Easy to install and simple to attach this aquarium heater to your aquarium via suction cups. Smart Thermostat Design: Fully submersible aquarium heater operates in intermittent mode. it is incredibly efficient and provides full, even heat distribution with no hot or cold spots. Fully Automatic