Hydor Betta Bowl Slim Fish Tank Heater, 7.5-watt, measures 3.5 inches round, black; For tanks 2-5 gallons

I looked at lots of heaters for small tanks before landing in this one and I highly recommend this little heater. I really like the flat design which I was able to “hide” it under the rocks at the bottom and my betta enjoys swimming around the cord. It’s also very simple to use: plug in and go. So far it’s been working well with no mechanical issues and the price is fantastic.

I originally got the 4w round heater for my Betta bowl, but it did not heat it to the temp I wanted (maybe a 5 degree increase), so I opted for the 7.5w which has been working wonderfully. I like the super slim shape which makes it easy to attach the heater to the back side of my Betta bowl behind the small filter that's also suction-cupped to the wall.The 7.5w heater has consistently kept the temp between about 77-81 degrees. My Betta seems happier and much more active and is eating more, so I believe the heater is making a positive improvement.There are no temperature controls for the heater, so if you want to be able to set a specific temperature, this may not be the heater for you. But if you are trying to increase the temperature by about 10 degrees in a small fish bowl or tank, this should work great.Some other reviews mentioned they'd gotten shocked when putting their hand in the water. That happened to me as a child when we had a really sketchy pump from a garage sale in our pond. So I stuck my hand in the Betta bowl to test and did not get shocked. The instructions do state that the heater should be unplugged before putting anything in there, but I wanted to note that the heater is well-made and designed to be submerged so it probably won't shock you. But better safe than sorry - just unplug it first.I'm really pleased with this little heater. It does exactly what I need it to do, it's inexpensive and works great. If you're torn between the 4 & 7.5 I'd monitor your water temp to see how much you need to increase it and choose accordingly.

Based on the product description, I ordered the size recommended for my 2.5 gal tank. Most of the time, however, I've had to keep the heater unplugged, as the temp climbed well above 82. As a result, I only plug the heater in on very cold days (house temp below 70), at which point it sustains a temp roughly 78.I do love this heater's slim profile and the fact I can bury it beneath the substrate. The cord isn't visible, as it blends into the black background on the back glass.I wish there was a way to control the temperature of this heater, or better yet an integrated thermostat that kicked the heater on and off as needed--that would make it perfect. Honestly, I was too lazy to dig it out, return it, and order the smallest size, which might have been able to stay plugged in all the time without overheating my tank. But for the time being, I've been able to keep the temp of my tank steady enough with just intermittently turning the heater on as needed. To avoid this hassle, I'd recommend ordering the size down (not the 7.5 watt, 3.5-inch round) for a 2.5-3 gal tank.

I've purchased 3 different types of Betta heaters for the various Betta I take care of. This particular heater advertized that it "Helps guarantee your fish a healthy life" but let me tell you how wrong they are. This is the only heater out of the 3 that I've used that has actually burned my Betta's fins... Quite badly. He was a beautiful fish and it was sad to see him suffer like that. This is in no way a safe heater for your Betta. I don't usually like to write 1 star reviews, but I really want to warn those of you out there looking for a heater not to get this particular product. It will damage your beautiful Betta if not kill him. The other heaters I'm currently using are the Marina 8w Betta heater and the National Geographic 10w & 25w heaters. They don't burn the fish in any way and they are fully exposed to the fish. I hope my fish can survive the burns... Please avoid this product if you want your fish to actually have a "guaranteed healthy life."Update (5 days later): I removed the heater immediately after I noticed my Betta was burned (about 3 days after I got the heater.) At first I took my Betta to the local exotic fish and reptile store so they could tell me what happened to the fish and how to help it. They said that the Betta appeared to have been burned by the heater and informed me that they've seen this before. Apparently this frequently happens when people purchase a cheap heater over the internet. The store employees then recommended a product called Melafix by a company called API. They told me it was a 7 day treatment and could help regrow his burnt fins while preventing infection. However, 5 days later my Betta passed away from its wounds. I'm really sad about it. I hope this story prevents this from happening to a future Betta owner.