Hydor Betta Bowl Slim Fish Tank Heater, 4-watt, Measures 3″ Round, Black; for Tanks 1-2.5 gallons
$12.99
Price: $12.99
(as of Oct 18, 2025 10:37:01 UTC – Details)
Hydro Slim Heater helps guarantee your fish a healthy life by promoting the ideal water temperature. Specially designed with the innovative PTC Film (Positive Thermal Coefficient) element to heat the temperature of your bowl, aquarium or terrarium an average of 5 to 10-degree warmer than room temperature. Whether it’s a glass, plastic or acrylic tank with fresh or salt water, this product is great for creating a more livable environment for your Betas, Glowfish and many other kinds of fish and reptiles.
Is Discontinued By Manufacturer : No
Product Dimensions : 3 x 0.25 x 3 inches; 3.2 ounces
Manufacturer recommended age : 1 month and up
Item model number : T20401
Date First Available : August 6, 2017
Manufacturer : Hydor USA, Inc.
ASIN : B076D8BMDX
Best Sellers Rank: #31,587 in Pet Supplies (See Top 100 in Pet Supplies) #76 in Aquarium Heaters
Customer Reviews: 3.9 3.9 out of 5 stars 1,816 ratings var dpAcrHasRegisteredArcLinkClickAction; P.when(‘A’, ‘ready’).execute(function(A) { if (dpAcrHasRegisteredArcLinkClickAction !== true) { dpAcrHasRegisteredArcLinkClickAction = true; A.declarative( ‘acrLink-click-metrics’, ‘click’, { “allowLinkDefault”: true }, function (event) { if (window.ue) { ue.count(“acrLinkClickCount”, (ue.count(“acrLinkClickCount”) || 0) + 1); } } ); } }); P.when(‘A’, ‘cf’).execute(function(A) { A.declarative(‘acrStarsLink-click-metrics’, ‘click’, { “allowLinkDefault” : true }, function(event){ if(window.ue) { ue.count(“acrStarsLinkWithPopoverClickCount”, (ue.count(“acrStarsLinkWithPopoverClickCount”) || 0) + 1); } }); });
The Slim heater will increase the water temperature of mini aquariums up to 10 gallons by a few degrees compared to the ambient room temperature. The Slim heater can be used in glass, acrylic, plastic fish bowls and aquariums. Safe to use under gravel. Please note, Slim heaters are not suitable to be used in environments without water
Extra small slim heater is a great choice for Betta fish & suitable for fish tanks 1 to 2 1/2 gallons, measures 3″ x 0.25″ , 4 watt; Plug and Play universal fish tank heater; No temperature to set; slim heater provides warmth for betta fish without taking up much room.
Heater can easily be placed submerged in water or even under the tank gravel; The 90 degree angle makes this great for Betta acquariums; Safe to use in glass, plastic and acrylic fish tanks
Plug & play universal fish tank heater, the slim fish tank heater can be used in both fresh or saltwater environments
Easy to hide fish tank heater is ideal to use for betta fish, gold fish and glow fish
Customers say
Customers find the fish tank heater works well for 3-gallon tanks and heats up 1-gallon bowls effectively. The size is suitable for small tanks, and customers consider it a good value. However, the temperature control and heating efficiency receive mixed feedback – while some say it keeps the temperature right and heats well, others report it doesn’t warm the water properly and stops working after a few days. The product quality and value for money also get mixed reviews, with some finding it great while others describe it as terrible and not worth the cost.
9 reviews for Hydor Betta Bowl Slim Fish Tank Heater, 4-watt, Measures 3″ Round, Black; for Tanks 1-2.5 gallons
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echobunny –
Increases temp about 10 degrees
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.
Mike –
Great Little Heater!
I love this little heater! It’s very discreet takes up virtually no space because it is buried under a little gravel. I have a 1.5 gallon tank. Before the heater, the water was about 68 degrees. Now with the heater, my aquarium is at a perfect 76-78 degrees! My fish seem much more active and healthier with the heater. The only con (if it has one) is that the heater doesn’t turn off. Instead the heater is designed to be 5-10 degrees warmer than the room temperature. For example, if my room temperature is 80 degrees, I would expect my heater to be around 86-88 degrees! Way too hot! So just remember to unplug the heater when the room temperature gets too high, and you’ll be fine! Also, this product is marketed towards beta owners. But remember this will work fine with any tropical fish! Mine are mickey mouse platys!
RushManZer0 –
Guaranteed To Burn Your Bettas Fins
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.
Jojoleb –
A simple heater for small fish tanks
I am using the Slim Heater to heat my Back to the Roots Aquafarm, which is a 3 gallon tank and it works well. Since the heater has been placed in the tank, the water temperature has been kept around 78 to 80 degrees, which is perfect for Bettas.The Slim Heater is basically a flat disk that can be placed under the aquarium gravel. You then plug it into the wall and that’s it. There are no temperature settings and no fidgeting. It’s plug and play. This has the advantage of ease of use. However, be forewarned that there is no LED light to tell you that the heater is even on nor is there any indicator when it is heating. There are no temperature settings, but given that the temperature in the tank has been between 78-80 degrees when measured by a floating thermometer, my guess is that the Slim Heater set point is within that range.This one is built for ease of use and seems to do the trick for small tanks. I can’t vouch for the longevity, as I have only been using this for about six weeks, but so far so good. It is easy to use and, so far, has been effective. Recommended.
Pam Alonso –
ES BUENO EL CALENTADOR, YO LO COMPRÃ PARA UNA MINI PECERA, PERO CUANDO LO CAMBIÃ A UNA PECERA DE 6LTS YA DEJÃ EL AGUA TIBIA, FUNCIONA PERFECTO PARA UNA MINI PECERA DE 4 LTS O MENOS
Rhiannon –
I bought the 7.5 watt option for my 3 gallon mini-aquarium with live plants and it got the water to about 71 degrees F. I wanted the water to be a little warmer than that, so I more recently bought the 15 watt for my tank in time for winter. It gets the water to about 77 to 78 degrees F, which is right on the money for a betta. If your tank is smaller than 3 gallons, I would recommend the 7.5 watt. I have never had any problems with these heaters and I love that they can be concealed under the gravel. Two fins up from Sharky!!
Amazon Customer –
This heater has been keeping my soon to be 2.5g shrimp tank at a steady 78 degrees for over a week now. So, so far, so good! 😀 I now feel like I can safely add some shrimp without worrying about drastic fluctuations that will either chill them at night or boil them during the day.
Techfox –
I have 1 gallon tank for my betta . I bought this heater with the expectation that it can keep the temperature ideal for its survival . I have a thermometer that is immersed in the tank to monitor the temperature all the time . If I keep this heater switched on for some time, the temperature keeps on rising to reach over 29 degree Celsius. I was really shocked to discover this . I stopped the heater immediately as I saw it at 29.4 degrees . If I didn’t stop it , this might go way over that for sure .When I did some research on betta on internet, I found the ideal temperature range for betta is between 25.5 to 26.5 . The temperature must not go beyond 27.5 or fall below 22.5 degrees . Like lower temperature, higer temperature can also effect the betta health badly . Such high temperatures ( 29+) can promote the growth of microbes in the tank leading to diseases and secondly it increases the metabolic activity of betta which can lead to rapid aging .It looks like this heater is unable to detect the water temperature . The only thing it does is to keep on increasing the temperature. Is the manufacturer expecting us to sit 24/7 in front of the tank to switch it on / off to get the temperature in this ideal range ?I will not recommend this heater . It will be better to find another one that can maintain a steady temperature.Update – after extensive search on Amazon, I found this heater – Marina C10 Compact Heater, 10-watt. This Marina’s heater can be the best alternative and satisfy all the requirements of a good heater according to my experience.
simon –
Gave this 2 stars just for the fact it works…barely. Purchased for a one gallon tank, just to keep a few degrees warmer but no dice, . Was going to opt for the 15 watt version for a couple dollars more but without a thermostat option I didn’t want to cook the beta, worries are now void; maybe a one degree Celsius advantage, I can’t see any aquarium niche were this heater could be applicable, maybe one of those 1 litre beta bowls but shouldn’t be putting any aquatic life in anything that small anyway. Go 15 watts or with a proper controllable glass tube heater. (Use in line heater through power filter output tubing for 55 gal tank, that’s by far the best heating option) Not sure how they can claim the 5 gal stat, it’s product description fraud.Update: Decided to give this product another shot this time using a two gallon tank but with a lid, much better results. The enclosed tank heated 5 degrees higher than room temperature. But again with no shut off or variable thermostat, the only control variable is either water volume or accessibility to air for cooling.