Mini Aquarium Heater 25W Small Fish Tank Heater 25 Watt with Free Thermometer Sticker

My Betta tank is in my poorly designed bedroom, heating vent at the top of the wall around the corner from the main part of the room so it is always cold in here. I was having a hard time keeping the water temperature at a good level so I ordered this little heater. Within 15 minutes of installing it, the water temperature rose to 78 degrees and is staying there. Very easy to read, when it lights red it is warming the water, when it lights green the water is at the pre-set temperature of 78 degrees so you don't have to worry about adjusting it or turning off/on. Very affordable, small so it fits into a small tank, good quality materials, comes with a temperature strip. Definitely recommend!

This heater is very easy to use—no temperature settings or adjustments needed. Just place it in the tank, plug it in, and it starts working right away. It maintains a consistent preset temperature that’s suitable for tropical fish. It’s been running quietly and steadily with no issues so far. The build quality feels solid, and the indicator light makes it easy to tell when it’s heating. Perfect for anyone who wants a simple, hassle-free heater without worrying about calibration or adjustments. Great option for beginners or anyone who prefers a straightforward setup.

I bought this heater for my 5-gallon betta tank, and it’s been amazing so far. It keeps the water temperature stable and consistent, which is super important for my fish. It’s quiet, compact, and easy to install — just plug it in and it works perfectly. I also love that the indicator light makes it easy to see when it’s heating. My betta seems much more active and happy now! Definitely recommend this heater to anyone looking for something reliable and affordable.

Update: I have discovered that because my bedroom(where my 20 gallon tank is located) is usually warmer than the rest of the house it is contributing to heating the tank which is why the 25w is able to heat it. I have one in a 10 gallon in my living room where the temperatures are usually 70-72 and it only gets it to 75° which means the heater is functioning properly as a 10 gallon needs a 50w so I gave the rating an extra star from my original 3/5 since my concern was more of a user error but the suction cup is still trash lol I have one of these heaters in my 20 gallon and it keeps the tank nice and warm. When I first got it did fantastic at keeping the tank at 78° but now it keeps the tank at a consistent 80° which I don’t mind as much since my fish can handle it but my concern is if it’s keeping my 20 gallon at 80° what would it heat a smaller tank to? The suction cup it came with is terrible It kept coming off and floating to the top Thankfully I had some extra suction cups from a different heater that failed on me I would say if you are getting this heater test it without life in your tank first before hand in case anything happens.

I'm using this for a 3-gallon shrimp tank. It's tiny. It's cute. There is a very belt-and-suspenders approach to being sure this thing is working properly. It lights a little even when it's not heating the water (I expect it's not heating the water when the room is nearly 90 degrees in August). The light is really only visible when the tank is dark and there isn't too much light in the room, but it's a small square by the bottom, just to clearly indicate it is working. I like that assurance. The little thermometer, which is also tiny and out of the way, would be another indicator, again if it weren't August and showing the water temperature in the 80s without the heater. So you can be certain, if there is a problem, you will know. But the ambient room temperature does lead to another point. It's small and I don't think it's that powerful. For me, the room is never going below 70 degrees. I'm in an apartment building with a lot of elderly residents, and the super needs to keep the place warm bordering on hot for them. I need the heater. The water will get too cold for the shrimp without it. But not more than say 10 degrees below their comfort level. If you're thinking a tank in say a garage (I know some people who use that as an office and keep a betta there) and you're prone to reasonably cold winters, then this might not be the thermometer for you. The shrimp seem to think it's a nice platform to sit on. I usually find at least one perched on top. I like especially how deep I can store it and the suction cups keep it firmly in place. If I'm only doing a one gallon water change (they're shrimp -- they have a really low bioload so changing a gallon a week is fine) then I can keep it plugged in while doing the water change and it stays fully submerged the entire time.

Plugged this into a new 5 gallon and it warmed the water from 74 to 78 in a short time. I hope it lasts, for the price it's great so far.

I ended up returning this heater. I will either buy a different brand, or just move my betta tank away from the cold window. 1st issue: It recommends a filter with it. Wish I knew that before buying. Heater seems overall like a decent quality for the very cheap price ($7) but just FYI the product states it should be used in a fish tank with a filter, in order to move the water around. Otherwise the heat will stay concentrated in one section and not be effective. 2: Not reliable. I left the heater in a large glass bowl of water overnight and throughout the next day, but it did NOT keep a consistent temperature. The temperature measured between sometimes 78 to 79.5 or even hit up to 80 degrees rather than staying consistent. I noticed it had a hard time staying at temperature and the light would continually change every 30 min indicating that it was heating up again. 3: The section cup it comes with kept coming loose and the heater would float to the top. Helped me best to clamp it down using a chip clip.

I have a large glass bowl that I use as an aquarium for my small tropical fish and I got this heater to use in it because it is only 2-3 gallons in size and this heater is perfect for it. It works great! I have purchased small heaters before and had trouble with them i.e. not really able to control the temperature well, but this one seems to be working great and keeping the temperature right at the correct level for my tropical fish without overheating the small tank. So I am happy with it. It came with a free stick on thermometer which didn't actually work i.e. the temperature would not show on it so I pulled it off the side of the tank to throw it away and it left sticky residue on the outside of the tank which was difficult to remove. I think it was included so you could verify that it was keeping the temperature at the right level. So the small stick on temperature strip was a failure but using a regular thermometer in the tank shows that it is keeping the temperature at the correct level and the heater itself has a little indicator light which shows when the temperature is safe (green) and when it is too hot or cold (red) and that works. So I threw the temperature strip away because it did not work and with some difficulty I finally got it off the side of the tank. It left little sticky bits behind on the glass that I had to scrape off. But the little heater works great and has its own internal safety indicator light where red equals out of safe range and green means it is safe and that does work. But the external strip thermometer didn't work and when I tried to remove it from the outside of the tank it was difficult to get the sticky adhesive off the side of the tank as some of it pulled off the little strip and stuck to the exterior of the tank glass and was difficult to remove from the glass. So I threw the small thermometer strip away as it was useless i.e. no temperature showed on the strip after a full day but the heater itself is great.