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Hydor Submersible Glass Aquarium Heater - Original Theo

3.9 out of 5 stars 812 customer reviews
| 117 answered questions

List Price: $20.99
Price: $15.29 & FREE Shipping on orders over $49. Details
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25 Watt
  • High resistance - the first shatter proof heater
  • Shock resistant
  • Position vertical, horizontal and completely submerged
  • Graduated scale for precise maintenance of set temperature
  • No damage in case of running dry
10 new from $15.29 9 used from $12.99

$15.29 & FREE Shipping on orders over $49. Details In Stock. Ships from and sold by Amazon.com. Gift-wrap available.

Frequently Bought Together

  • Hydor 25W Submersible Glass Aquarium Heater - Original Theo
  • +
  • Marina Floating Thermometer with Suction Cup
  • +
  • Zoo Med Laboratories AZMBL20 Betta Hammock
Total price: $23.27
Buy the selected items together

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Size: 25 Watt

Product Description

Size: 25 Watt

Product Description

Theo Heater. New aquarium heater functioning with the exclusive PTC technology means that this heater will not break or damage when run out of the tank. Theo aquarium heater has all the necessary feature for safe and precise temperature maintenance of the water in your tank. The exclusive technology and the high quality of components guarantee a long lasting product.

Manufacturer's Notice

http://www.cpsc.gov/cpscpub/prerel/prhtml11/11202.html

Product Details

Size: 25 Watt
  • Product Dimensions: 3.5 x 2 x 10 inches ; 8 ounces
  • Shipping Weight: 8 ounces (View shipping rates and policies)
  • ASIN: B0006JLPG8
  • Item model number: T11702
  • Average Customer Review: 3.9 out of 5 stars  See all reviews (812 customer reviews)
  • Amazon Best Sellers Rank: #4,008 in Pet Supplies (See Top 100 in Pet Supplies)
  • Manufacturer’s warranty can be requested from customer service. Click here to make a request to customer service.

Customer Questions & Answers

Customer Reviews

Top Customer Reviews

Size: 25 Watt
I bought a Marineland 10W heaters for my 2.5 gallon tank, but found that it overheated the water way too much. That heater may have a sensor that tells it when the water temp is too cold, but it does not shut off when the water temp skyrockets above 78 degrees Fahrenheit.

This heater, on the other hand, while larger and more obtrusive, does a much better job in regulating water temperature. I never have to worry about finding my tank temps in the high 80s the way I did with the other heater. Also, the fact that it has a regulator dial is a huge plus. While the dial calibration may be off by a degree or two, it does work. You turn it up, the water temp goes up (but not too high). Also, the little indicator light is a nice way of checking that the heater is on and working.

Even for small tanks, I would skip the unregulated 7.5W and 10W heaters and go with this one.
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Size: 25 Watt Verified Purchase
I was only hesitant to purchase this because I needed to use it for a ten gallon tank (It's designed for a 7gal) and this was the most affordable option. I urge you to not be anxious yourself, however, as this heater is splendid. It looks reasonably nice and will heat your water (even in a ten-gallon tank); what more can I say? If you need an aquarium heater and have a 10gal, don't sweat it. Just buy it.

Also, it's worth mentioning that the heater doesn't look exactly like the one in the main picture. It's shorter and fatter (proportionately at least...) than pictured. This isn't a bad thing. Just don't freak out, because you ARE getting what you ordered.
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Size: 25 Watt Verified Purchase
I really like this heater, even though it is costly for its wattage.

Small tanks, typically used for Bettas, always have the issue of heating them and due to their small size most heaters will not fit. Well, this small 25W heater works perfectly in my 5.5 gallon aquarium easily fitting vertically with plenty of space to spare above and below. The thermostat on top is labeled in temperature, versus just a + and - or arbitrary scale (like 1 to 10). The temperature may not match the dial right out of the box, but really that's not a big deal. If you need it a degree warmer, you turn the dial up 1 degree. This is assuming you are not exceeding the capabilities of the heater, which I explain in more detail below.

I'd like to point out that this is a very low wattage heater. So while it works fine on my 5.5g aquarium you should know that it will only do fine if your room temperature is somewhat close to your desired tank temperature. If you keep your tank at 78 degrees, but in the winter your house is at 65 degrees this heater will not be able to make up the 13 degree difference. Small tanks loose heat fast, and this heater at just 25W will not be able to keep up with that.

Because of this some people will mistakenly say "It can't heat my tank even when I turn it up to high". As I mentioned earlier, these have a thermostat so they work only on temperature. If it is set for 78 and the tank is only getting up to 76, it is doing its best to heat the tank to the set 78. Turning it up to 85 degrees does not change that. The heater will not turn on, and stay on 24/7 and the reason is so that it doesn't super heat itself.

How low your house can be for this to work will depend greatly on your specific tank dimensions, what's in it, and your filter flow.
Read more ›
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Size: 25 Watt Verified Purchase
This heater has worked great so far. I've had it heating my 3 gallon tank for about 3 months now and I am very pleased with it's performance. It has done a fantastic job keeping the tank at a constant temperature. When the air temperature around the tank changes, tweaking the heater's adjustable temperature setting is quick and painless (just turn the dial a bit!).

I bought this product because I was going into an apartment with roommates who I knew wouldn't want to pay to keep the air temperature at Betta-friendly levels. So I spent months looking at the different options on Amazon and trying to make heads or tails of which tank heater I should get and being very indecisive. In the end I decided to give this heater a try for it's cost, adjustable heat setting, and the overall positive things I was reading in people's review.

Although the temperature on the heater control does not usually match the temperature on my tank's thermometer, this hasn't proven a problem at all as it just requires me to tweak the heater's control until the tank thermometer shows the water is at the temperature I want. Therefore the fact that heater and thermometer are at different temperatures is inconsequential. The heater is doing it's job and keeping my tank at Betta-friendly temperature
So this is a solid choice for consideration in your search for a tank heater.

The positives and negatives so far
Positives: submersible, temperature control, keeps tank at a constant temperature
Negative: if the air temperature outside the tank changes you may have to tweak the heater's temperature setting, temperature set on the heater may not match the temperature in the tank
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Size: 25 Watt Verified Purchase
This is the perfect heater for my 2.2 gallon Mr. Aqua tank. Keeps my tank at 78 degrees in a room that is barely over 60. I live in North Dakota in a converted cabin so I was afraid it would not be able to maintain heat. It does and well. I have it set on the dial for "79" degrees but it holds the tank at 76 to 79 degrees depending on if my room heater is on or not. Small footprint and easy to hide in my small tank. Light comes on when it's heating.
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