Review on Hydor Slim Heater for Bettas: Optimized for Bowls and Aquariums by Jennifer Duncan

I have this in my beta bowl. It's not a huge environment, but it does have a fairly large surface area for its size (i.e. it's fairly flat). A full bowl probably holds about 1 1/3 gallons, it probably has about a gallon in it as of this writing. I keep the heater buried in the gravel (well actually the gravel is stacked in it but not on top of it) and the cord runs down the side of the bowl which is attached with a suction cup (which comes with the unit). Don't keep daily temperature logs, but a quick glance at the thermometer in the bowl shows it's right around 74F. I think when full it keeps it around 70F. The thermometer probe is mounted opposite the heater. The entire unit is in a heated office which is kept at room temperature and circulated by ceiling fans so it's a fairly stable environment. Since the heater is on full power all the time and doesn't have a thermostat, the temperature naturally fluctuates depending on the environment. Overall the heater seems to work well for what it is. It's unobtrusive enough not to disturb my fish even in a small bowl, puts out just enough heat to keep it brown, and I love that I can just pull it out and put it aside without burning it when I need to clean the bowl. (It shouldn't be damaged unless it's submerged in water and the cord slips out of the little clip on the suction cup so you don't even have to open the suction cup). I'm happy and my fish are happy, but I have to admit my needs weren't great. In a real aquarium (or even a larger bowl) or an environment with fluctuating temperatures, this obviously won't work, if at all.