Review on High-performance Hygger Titanium Aquarium Heater: Fast Heating & Digital Temp Control for 60-180 Gallon Freshwater Marine Tanks by Amy Smotherman

I needed a compact immersion heater to keep the water warm in a small 4 gallon stone fountain we have on our porch. Our winters are not terrible where I live, but the temperature sometimes drops to 20 degrees and even to teenagers. We have some goldfish in the well and wanted to "hibernate" them there. This heater is small and flat and was able to reliably keep the water at 68. Actually I would have preferred it to be a bit cooler for goldfish, but 68 is the lowest setting and the fish tolerate it well. It heats water without a heater, which is a "hot spot". The controls are intuitive and easy to use. A word of caution. It is important that this heater has water flow from all directions. I laid it flat on the bottom of the fountain and it worked for a day or two and then shut down with an error code that it was 'no water'. I unplugged it, took it out of the water for a few minutes, plugged it back in and it restarted and worked fine only to have the same error again the next day. I finally found out that when he's lying flat on the floor he can't tell the temperature and thinks he's overheating. Propping it up just 1/2 inch off the ground with a small rock was enough to fix the problem and it's been working great ever since. with two other thermometers) and it doesn't change more than 0.1 degrees throughout the day from warm days in the 50's outdoors to very cold nights in the 20's.