M 150-Watt Submersible Aquarium Heater – Reliable, Compact Heating with Mirror Technology for Fresh & Saltwater Tanks Up to 45 Gallons

I love this heater. I have been using it in my betta's tank for about a year, and so far, it has worked very well! This heater is not made for being completely submerged under water. The black and grey part (the part above the little wavy marks) must be above water, along with the cord. I put this heater right next to my filter so that the filter motor can move the warmed water around the aquarium evenly. This heater is, of course, automatic. It has a thermostat somewhere in it that tells it to turn on when the water is too cool and turn off when the water gets warm enough. When the heater is warming your tank water, there will be a blue light on the side, and when it turns on and off, it will make a clicking sound and the light will turn on or off. This is a very good heater for my five-gallon tank. I have it set at about 81 degrees, and it keeps my tank at a steady 78 or 79 degrees Fahrenheit (which is the perfect temperature for betta fish). I am very impressed!

I really like how oversized these are it seems efficient - getting these dialed in on the temp requires another thermometer imo that is calibrated And I think the safest bet is an ink bird or equivalent as a backup thermometer Incase of it breaking and ending up stuck on - I don’t do this (maybe yet?) but for an exspensive or huge tank I would consider it

Works great

(SECOND UPDATE, 10/19/12) After a year of use -- completely submerged -- the second heater continues to work as well as it did when new. Some samples, like my first one, may suffer from initial quality control issues, but Fluval M's remain excellent heaters on balance, holding their own against any on the market (and I've used most brands at one time or another). (UPDATED 11/9/11): These are nicely designed, sturdy heaters with strong borosilicate glass, quality interior components, and sleek contemporary appearance. Unfortunately, Fluval's "computer calibrated thermostat and 16 point quality assurance" do not necessarily deliver the promise of their engineering. The first one I got was defective out of the box. No matter how I adjusted the controls, the lowest temperature it would maintain was 84 F., much too high for most fish on a sustained basis. The thermostat is of high quality, with less temperature variation than most, but the poor calibration made that irrelevant. Since Fluval has been a reliable brand for decades, I decided to try a another one. The second Fluval M has worked perfectly so far (about three weeks). The preset is off a couple of degrees, but that is within normal tolerance for aquarium heaters. I would certainly recommend one of these, provided it is purchased from a source (like Amazon) with a liberal return policy in case you receive a defective sample. My guess is that if you get a good one initially, it will provide many years of reliable service. As an aside, I'd like to offer some comments about a couple of other matters mentioned by various reviewers: Contrary to what Fluval implies, they don't disappear into their surroundings in the aquarium. They are nice looking, but quite conspicuous, more so than the dull charcoal gray finishes commonly used. They are no easier to hide from view than any of the eight other heaters I currently employ. Fluvals are as fully submersible as any other "submersible" heater. Fluval representatives have stated that the instructions and high water line indicator were required by Canadian government regulations, presumably as a safety precaution. (Fluval's distributor is headquartered in Montreal.) It is prudent to keep the top of any submersible heater above water, and I do so when the aquarium design permits, but because of the layout of the tank it is in, this one is fully submerged. I could readily switch it to one of my other tanks where the top would be above water, but haven't bothered. I don't believe this "issue" should be a reason to avoid the Fluval heater.

Really like this product very heavy seems to work very well

This Fluval heater is a solid piece of equipment. I’ve had it running for almost 2 years now and it’s still performing like a champ — keeps the water at just the right temp without any fuss. The borosilicate glass design is a nice touch — it blends into the tank much better than those bulky, obvious heaters. You can still see it, but it’s not screaming for attention. The temperature dial is easy to use and overall it feels well-built and dependable. If you’re looking for a heater that just works and doesn’t make your tank look like a science experiment, this is a great pick. Its a good size, nice and slim and definitely worth every penny.

I just removed over 30% of the dirty water which I could have done a lot more, but didn’t thank heavens. I cleaned the tank and accessories to give it a fresh start for my new heater. The temperature dropped rapidly as I replaced the water but I had installed my new Fluval 100w heater for the 30 gallon tank I have. Then I started to panic as I was counting on the heater to bring it back up to the correct temperature. Instead, nothing. I followed the troubleshooting directions to no avail. In the return process, it asks if I’ve removed the item from the package and if I have the original packaging which I do, but it concerns me that they will just send it out to some other unsuspecting aquarium hobbyist. I highly recommend if you order this item, which unfortunately I cannot recommend, to test it out first before you did what I did. Make sure it’s covered as indicated in their directions in a container of water beforehand. My fish is 6 years old. I thought Fluval was a trusted brand. I also had issues with their HOB filter for this same tank. It clogs easily. I returned from a 10 day trip to Europe only to smell smoke coming from the room where my tanks are. The filter had overflowed and water ran down the back of the tank, onto my area rug and hardwood floor. Worst though, was it dripped onto my surge suppressor and was smoking! Ironically, the surge suppressor came from Amazon too as some obscure Prime Day deal. Well, that also was replaced with the trusted Belkin name. During this incident, I had a pet sitter come while I was gone so it’s not like I left them with no supervision but really?? Who knows how much longer until a fire could have broken out. This was during the time Fluval acquired Aqueon. And of course it wasn’t returnable through Amazon so I had to suck it up and buy another filter. But I went with the Tidal brand which I have in my 72 gallon tank. To get functioning, reliable items has been like rolling the proverbial rock up a hill. It’s the cost, time, and aggravation that is exhausting. I thought Fluval was a trusted brand? For me, it’s been problem after problem with several of their products and it’s just exasperating. I need a reliable aquarium heater. Not one I that I have to worry about. So now I have schlep this broken heater back to Staples and find a reliable heater. Like this shouldn’t be so hard. Oh, and if you pre-test it as I suggested, there is supposed to be an indicator light. I can’t say where it’s located as no light ever came on. But make sure your light works. And obviously you can feel when the heater warms.

This M series 200 watt heater is a bit overkill for my 32.5 gallon tank. But it works great! I however wouldn't rely on the temperature setting gauge on the device. The best way to properly setup a heater is to set it to come on at just the right temp you want it at. Then monitor the temps over the next few hours and raise or lower the dial to match the actual temperature you want. The dials are seldom that accurate on their own. Try to attach the suction cups near the top. Don't have the holder setting on the coil area as it can melt the plastic. Also don't let the heat bulb touch anything near it. It can damage whatever it touches and can be damaged if something is leaning on it when it turns on. Place this heater away from invertebrates and snails. They can be burned or killed if the heater turns on when they are crawling around on it. These M series Fluval heaters are good heaters and I've used different wattages of them for years. But if you use them, pay attention to your tank's temps. If they stick on, they can cook your inhabitants. If they don't turn on, your tank temp could also get too cold. These heaters also are not intended to change the temp of the tank water more than 10-15 degrees total over time. They should not be used for outside use or when the room temp is way below the temp you want your tank water. They are designed to heat a few degrees only. Be sure the glass tube is not cracked or broken. Water must not contact the inside of the tube.

This is an amazing heater, I’ve gone through probably 5 different brands of other heaters that won’t keep a consistent temperature or won’t even work in general. Saw a recommendation for this brand/model and I love it! Super easy to use and to adjust temperature. Highly recommend

Formschön und einfach in der Handhabung. Sehr gut.

Très bon chauffage, aucun regret sur son efficacité

Better to buy a local heater from your near buy aquarium store .No proper warranty support provided by the co and seller in India .The co says to reach out to the seller to claim the warranty and the seller says one has to go to the co to claim the warranty . Beware all the aquarium enthusiast .

As expected from a well known company for aquatics.