I've had a 500 gal pond for 15 years! I use these because they are available locally. This is important because they fail so often. I've sent 3 in for failing under warranty, but this is such a hassle. I've now gone through about 12 of these. They just don't last. They either just stopped working (ice in the pond), or trip the breaker because they are water logged. I live on the Eastern Shore of Maryland, it very seldom freezes here, so they are only use 2-3 months a year. I'd suggest another brand, they seldom last more than a year! I have another brand (exposed elements) which I've used for "backup" for 10 years, with no problems. I just don't like the exposed elements.