Tetra 26446 HT Submersible Aquarium Heater With Electronic Thermostat, 100-Watt, Multicolor, 10-30 Gallon

Small yet mighty
Small but works good. Temp is accurate.

Update: Broken after 2.5 years and Tetra still honored warranty
Update 01/19/2018: I contacted Tetra for troubleshooting. Although the warranty says 2 years and my broken heater was purchased 2 years and 6 month ago, they still honored the warranty and sent me another one. Because of their awesome customer service I moved the star from 2 to 4.
Update 01/13/2018: After a little over 2 years, I found that my 5 gallon aquarium water was evaporating real quick. (1/4 water was gone in 7 days.) I did a quick check and found out the water was 92 degrees Fahrenheit! And still the water heater was “red” (meaning it was still heating up my tank. Thankfully none of my fish were dead as I quickly unplugged the heater and inspected it and I cleaned the outside of the heater thinking that there was a buildup near the sensor. I plugged it back in after a water change which lowered the water temperature back down. After 3 hours of continual heating my aquarium is once again around 83 degrees. The sensor seems to be broken. Barely lasted over 2 years. All I did was plug it in. I have heaters that lasted over a decade. This is unacceptable in my standards. Never again am I buying tetra products for my aquarium needs.
Original purchased 05/24/2015
When I got this item, I put it in the aquarium horizontally and left it in the tank for about 6 hours so that the water temperature will match the inner core of the heater’s internal thermometer. And then I plugged it in with my fish in the tank although the manual said not to put fish in until after 24 hours have passed and the temperature is steady. I kept an eye on the temperature for about the first 12 hours. The room temperature was around 65 degrees the moment I plugged in and it rose to 80 and the air conditioning kicked in lowering the room temperature. This heater kept my aquarium consistent 78 until the room temperature got 80 which raised my aquarium to 79 degrees and when the AC kicked in it kept the water at 78 degrees. It has been 2 weeks since I had this and I have no issue for my 5 gallon aquarium. Good value for the money. 5 stars

Worked for 2 weeks!!!
Got this 2 weeks ago and was thrilled that it kept my 3 gallon tank warm and my betta happy… until it stopped working last night after I cleaned the tank and changed partial water. It stopped working all together and water is ICE COLD this morning! The light is green and will occasionally turn red for a few seconds before going back to green (which is supposed to indicate the the water is at the correct temperature). Still cold. I called Tetra customer service after reading many of the reviews here with the same issue. I explained what happened and asked if there is anything I could do to fix it or reset the heater as another reviewer mentioned that customer service gave instructions which fixed the issue. The customer service rep I spoke to would not help or even talk to me further if I could not tell him the temperature. I explained that I do not have a thermostat therefore I wouldn’t be able to check the temp but I assured him that the water was noticeably cold to touch in comparison to the warm water that has been consistent in the tank in the 2 weeks I’ve had this heater and tank. He rudely continued to cut me off and said that he couldn’t help me if I don’t have a temperature and he became more and more condescending in his tone has he continued. His customer service was TERRIBLE! I told him that I understood he needed to know the actual temp and that he couldn’t trust the temperature based on touch, so I asked if he could at least tell me what the possible options are as far as fixing this issue would be as I saw many other amazon reviewers shared the same issue. He became increasingly frustrated, increasingly rude, saying that he needs the temperature to know if he needs to send a replacement etc. I graciously explained that it was not my intention to get a replacement. I just wanted to know if he could help me troubleshoot so that I can attempt to fix my heater before my betta dies. I’m not interested in waiting for a replacement heater to come in the mail. Eventually I just asked to speak to his supervisor multiple times before he finally he basically said (like a child with a bad attitude) “Fine…..” and he patched me directly through to someone’s voicemail. I WILL NEVER PURCHASE TETRA PRODUCTS for the simple fact that customer service is NOT a priority to them. A simple “I’m sorry you’re having trouble with your new heater. Tell me what’s happening and let’s see what we can do….” would have been great and I would be willing to go to the nearest pet store and buy a replacement myself if he was willing to help me troubleshoot and exhaust all options first. Instead, the gentleman has no customer service training, does not know the meaning of showing empathy, and is not interested in helping anyone… unless you can tell him the temperature of the water even though this heater doesn’t have a thermostat in the first place.

Does the job
Product is just as described. Works well in our 10 gallon aquarium. Price was much better than box stores.

This heater works fantastically.. I ordered it for my 3.7 gallon aquarium and it had no trouble heating the water up to 76° and maintaining that temperature even in winter when the indoor temperature in my house can drop to about 60° or lower.
It has a long cord so you don’t need to have your aquarium by the power source which could be dangerous.
It secures to your tank by a suction cup which is very strong.. if secured correctly the heater will not come off.
Good heater at a good price.. it works great can’t complain.

This heater has worked great after my last one died suddenly. It doesn’t have the option to change the temperature, but for my needs, that is no issue. I do hope there is no chance for the regulation to fail, however, I have it plugged into a temperature controller anyway, so I will know if it goes too high or too low. So far no issues. Using it in a 10-gallon tank.