Hydor Theo Shatterproof Aquarium Heater, 25-watt

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$26.89 (-25%) Chewy Price
$35.95 List Price
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Arrives between Jan 25 and Jan 31
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About This Item

Details

  • A fully submersible, shatter-proof glass aquarium heater.
  • This heater is shock resistant thanks to the patented PTC heating element and the shatterproof glass tube.
  • The supplied suction cups allow you to position the heater anywhere in your aquarium. You can place it in the fish tank vertically, horizontally and fully submerged.
  • If heater senses abnormal functioning, the patented PTC heating system guarantees completely safe operation in case of dry running.
  • This universal aquarium heater may be used in freshwater or marine water fish tanks.

Instructions

Size

Learn More About Hydor From Our Team of Experts

Questions & Answers

6 Customer Questions

Can the temperature be adjusted?

Answer by Chewy • Oct 20, 2017
The temperature can be adjusted.

What neater is best for a 5 gallon tank?

Answer by Chewy • Aug 25, 2018
The 25 Watt Aquarium Heater is ideal for 2 - 7 gallon aquariums.

What is the length of the heater?

Answer by Chewy • Apr 06, 2024
The 25-watt heater measures 7 inches long, the 50-watt heater measures 7 inches long, the 150-watt heater measures 12 inches long and the 400-watt heater measures 15.5 inches long.

Can this thermometer be used in a turtle aquarium?

Answer by Chewy • Aug 26, 2018
This heater is suitable in saltwater and freshwater tanks.
Reviews
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3.5
Rated 3.5 out of 5 stars
42 Ratings
Terms & Conditions

38 Customer Reviews

Rated 1 out of 5 stars
By The on Jan 20, 2025

Fish Fryer

It worked great for a couple months. Fast forward. Noticed my tank was holding a higher temp than it should. I had dialed it back to 75 but it registered at 84

It worked great for a couple months. Fast forward. Noticed my tank was holding a higher temp than it should. I had dialed it back to 75 but it registered at 84. I kept dialing it back and even got to the point I was leaving off lights and blowing a fan at the tank to cool it. Other day while I was out of town, hubby suddenly notices my fish acting odd struggling for oxygen. He didn't know how to help the little guy. He took out the heater and it was HOT to the touch he said. He had a heat gun that told him the temperature of the heater was at 95 degrees and the water in the tank (by his read and the thermometer read) was at 88. He removed the heater. Little late and my fish struggled for a while before passing. When I returned home I looked over the heater. Burn marks all over it. Biggest mistake I've ever made for my fish was absolutely buying this heater and thinking to not check other reviews. Please heed my warning and RUN don't walk FAR from this brand.

Rated 1 out of 5 stars
By Kaitlin on Dec 1, 2024

Glass broke

I bought it last year and never used it (it got too warm by the time I got it) so I took it out the box this year and have been using it maybe a week. Checked on

I bought it last year and never used it (it got too warm by the time I got it) so I took it out the box this year and have been using it maybe a week. Checked on my turtle this morning to find the heater has shattered inside the tank. Very dangerous for not only myself but what I’m worried about this most, my turtle..

Rated 5 out of 5 stars
By Asenath on Aug 26, 2025

Reliable

Good quality

Good quality

Rated 3 out of 5 stars
By Rebecca on Nov 3, 2024

Poorly packed

Glass heater rattling around in shipping box with no packing which could have damaged the heater.

Glass heater rattling around in shipping box with no packing which could have damaged the heater.

Rated 5 out of 5 stars
By Kirstin on Jan 16, 2024

Exactly what I needed

I have a Betta fish and needed to keep the temperature around 75-80 and my house is typically 60-62 so I needed something more powerful than I was recommended. Returned

I have a Betta fish and needed to keep the temperature around 75-80 and my house is typically 60-62 so I needed something more powerful than I was recommended. Returned the original and got this one. Works great and has kept the temp right where I’ve set it.

Rated 5 out of 5 stars
By Kelley on Feb 6, 2024

Turtle loves

My RES is loving her warm water hopefully she won’t break the heater this year

My RES is loving her warm water hopefully she won’t break the heater this year

Rated 2 out of 5 stars
By Betty on Oct 10, 2022

Be Cautious

Ordered because I wanted a heater for my 5 gallon tank that I could adjust. I didn’t read all the reviews. My experience was similar to most of theirs. I set the

Ordered because I wanted a heater for my 5 gallon tank that I could adjust. I didn’t read all the reviews. My experience was similar to most of theirs. I set the heater to 79 and went to bed. Next morning I found it had heated to 84. First, I adjusted it to 75, but it still wanted to turn on. So, I unplugged the heater and waited several hours for the water to cool down to 79. Then, I turned the heater setting to 68 and plugged it back in. Over the course of 2 hours, I turned up the heater setting a degree or two until I knew it was keeping the water a consistent 79. That setting, for me, was 75. For looks, I love it. It’s slim and modern. Price was great. But, just be aware of it’s possible issues and keep an eye on it until you’re confident it’s working properly.

Rated 2 out of 5 stars
By Kat5 on Dec 31, 2018

Stuck on one Temp

This aquarium heater worked great for a few months. The design and appearance are great, but after a while I noticed that even if I had it on its lowest setting

This aquarium heater worked great for a few months. The design and appearance are great, but after a while I noticed that even if I had it on its lowest setting (68) it kept my tank was stuck at 82 degrees F... didn't hurt the fish at all, but had I owned fish that enjoyed a slightly cooler temp, I would've been in trouble.

Rated 1 out of 5 stars
By Mike on Dec 28, 2018

waste of money

My experience with this product was very DISAPPOINTED after buy 4 units "1 per aquarium" fully submerged in less then 2 months 3 units just burn . I call the manufacturer

My experience with this product was very DISAPPOINTED after buy 4 units "1 per aquarium" fully submerged in less then 2 months 3 units just burn . I call the manufacturer and they have a only 30 days guaranty. And the last unit is a PAIN,,NEVER KEEPS THE RIGHT TEMPERATURE,,NOT A RELIABLE BRAND!!!!!

Rated 5 out of 5 stars
By Jennyw on Dec 14, 2018
Top 50 Contributor

I don't trust other heaters

Sad they seem to be phasing them off of Chewy. They are all I use and so far they always seem to maintain the correct temps.

Sad they seem to be phasing them off of Chewy. They are all I use and so far they always seem to maintain the correct temps.