DaToo 20 Watt Small Aquarium Heater Mini Betta Flat Fish Tank Heater for 2 Gallon 3 Gallon

This is a great product, easily kept my fish tank at 80 degrees Fahrenheit and had no problems. The only issue is that it is missing the thermometer it promised would be included. Other than that, this product is amazing for small tanks like 1 gal and higher.

This unit is supposed to automatically adjust to conditions and keep the tank in the happy zone for betta and other tropical fish, but it DOES NOT WORK as advertized. It works well in cold rooms to keep the temperature warm in the tank, but if your room heats up, the unit continues to provide additional heat, cooking your fish in the tank. I am so angry at myself for not noticing the signs earlier. For the record, my room never got above 75-80 degrees Fahrenheit, but looking at the temperature in the tank, it's currently 88 degrees. If you have some other low intensity heat application you need this for outside of fish care, it may suit your needs, but if you value the well-being of your bettas, keep well away from this murder device.

Our 3 gallon tank stays about 82 degrees in an old drafty house where the thermostat is set somewhere between 64 and 68 all winter. Our betta is delighted! I imagine that I'll need to switch out heaters come summer/fall when we keep it warmer in the house, but I'm pleased enough with this one that I'll stick to the same brand/type.

It works fine but I see the temperature fluctuates quite a bit between 72-85. Not sure if it’s because of the temperature of the room or what? Also, with only one suction cup at the top the heater flops around in the water

I got a 2.5G tank and thought I'd be fine with one of these "plug it in and forget it" heaters. Nope. I don't know why anyone would be satisfied just letting it go without any control; plus, the digital thermometer it includes? CRAP. Do NOT trust it. It sits underwater WITH A BATTERY! The screen is SUPER sensitive to touch and it's just not worth it. You're better off with one of those cheap liquid crystal stick-on jobbers. Overall there are much better small heaters out there with reliable temp control.

Nice and thin and works great on a 5 gallon tank

Slim design made it east to hide in the filter so it didn’t clutter up our display tank.

Crapped out in a month. No longer works as well as the thermometer that was waterproof is now waterlogged and I can no longer read it. Junk.