Review on BinChang Aquarium Heater - 100W/300W/500W/800W Quartz Glass Fish Tank Heater with External Temperature Controller - Explosion-Proof Water Heater for 5-158 Gallon - Suitable for Marine and Freshwater Fish Heating by Tracy Anderson

I use this heater (500w) to heat a 120 gallon (preformed) pond and it's holding up pretty well. I bought a heater and made the mistake of trusting the sticky part to stay on the wall when installing it. Okay. the thermostat fell into the water and all the numbers were messed up and my switch broke. I ordered another one and made sure the thermostat was off the water. The heating works great, but I have a recommendation for the first start. If, like me, you have a large cold pond, I recommend adding two heaters first, waiting for it to reach the temperature you want, and then deciding whether or not to take out the second heater. If you try to use this alone to heat 120 gallons from 60F to 80F it just won't work so I started with two heaters and then took the second one out when it reached 80F. Since then, this heater has maintained this temperature without any problems. Cheap and worth it.