Q: Anon wrote,

With the colder weather coming I’m noticing my aquarium temperature is fluctuating a lot and it gets pretty cold at night. What kind of heater do you recommend for a 3 gallon tank?

A: Ah yes, with Autumn comes cooler weather and fluctuating aquarium temperatures that can lead to stress or illness. I just installed my aquarium heaters in all my tanks, which I had removed for the summer. For a mini tank from 3 – 6 gallons I find an adjustable 25 watt aquarium heater to work very well. For such small volumes of water, that adjustability is key. Bettas, being completely tropical, require a steady water temperature between 78 – 80F [25.5 – 26.6C] so it helps to set the heater low and to slowly warm it up as necessary to meet the desired temperature. If the existing water temperature is quite cool (around 70 -72 degrees) allow yourself a couple of days to get the temperature up to where you want it. Rapidly fluctuating temperature are much more destructive so don’t feel you need to get that temperature up immediately. Take your time.

There are several brands and styles available including fully submersible and partially submersible. I don’t have a strong preference between fully and partially submersible but I do prefer one that is easily adjustable. Some can be tough to adjust and are hard on the fingers. The most important thing for me is an indicator light and the second most important thing are temperature indicators. (Numbers that actually say 77, 78, 79, 80 degrees etc.) They are almost always off somewhat but at least it offers a starting point. Some don’t have any indicator numbers and all and can require more guesswork then I like.

My favorite mini heater is the Marineland Precision Heater for Aquarium.

There is also this submersible flat pack mini-heater. I have never tried it and can’t endorse it but I would love to hear your product review if you have used this heater. Please feel free to post comments on this blog entry about this heater or other heaters you love or hate.

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Reader Interactions


  1. Carina says:

    I have two large bowls (I think 2.5 gallons) for my Bettas and have used these little flat heaters for the last three years – I got them at Pets Supplies Plus (midwest chain similar to PetsMart.) for about $8.00. I can’t attest to how constant a temperature they keep the water because I don’t use a thermometer…the water always feels mildly tepid, though. One of my fish is going on 4 years old and I’ve never had a health problem with either, they are frisky and eat well and make lots of little bubles so I assume they’re doing fine.
    Sorry it’s not a very technical heater review. 🙂 a

  2. Christie says:

    Carina, thanks for the review. I know I found it really helpful and I’m sure others will too. You don’t need to get much more technical with a 4 year old betta. It sounds to me like you must be doing a great job to have raised him up to be an old timer. Thanks again!

  3. kelly says:

    I just received a 100 watt Askoll IP68 tank heater with only a plus and minus rather then temperature indicator. I have a 4 gallon tank and one Betta fish. Is this too much for the tank and how do I use it?

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