Hydor 100W Submersible Aquarium Heater - Original Theo

The unit consistently delivers the same temperature, which is good, but that temperature is always about five degrees higher that where I set it. So if I want my tank at 77 I need to set this to 72. These products are all about accuracy and consistency, and this unit has not been so great. I'm too lazy to make a warranty claim, but I figured other customers should know my experience.

I got this heater with a fish tank that we purchased. It was keeping our 65 gal tank about 80, but when I saw where the dial was set, I moved it to 82, and it made my tank go to 90 degrees! I was shocked when I saw the temp. I had to do some fancy footwork to get the tank down to where it should be. I will be buying a new heater. Accuracy is important. I would not recommend this heater.

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Bought two of these for my 20 long freshwater tank (I put one on each side.) They practically go on and off at the same time that's how well calibrated they are. In my setup, they have about a 2-degree range from where I calibrated them meaning, I set them both to their highest settings initially and after an hour I plugged them in, and then turned them both down until they turned off at the temperature I wanted (79 degrees.) The tank fluctuates between 78+ and 80+ degrees, which is very acceptable to me.

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I bought this product thinking that it had good ratings then I put it in my tank the water was always over 80 degrees F even when it was set at 75 degrees!!!!!

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The hydor THEO line of heaters is great. they're not HUUUUUUGE and they get the job done.

they consistently maintain the temperature of the water.

i have comparable heaters but they're as long as my elbow to the tips of my fingers. the theo is nice and small and you can fit it in just about any aquarium.

it also does not pop or make other noises like aquion heaters.

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