HYDOR Theo Shatterproof Aquarium Heater, 400-watt - Chewy.com

Hydor Theo Shatterproof Aquarium Heater

By Hydor
Rated 3.4062 out of 5 stars

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$34.99Chewy Price
$54.45Chewy Price

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About This Item


  • 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.

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Questions & Answers

7 Customer Questions

What is the cord length?
Answer by ChewyNov 03, 2017
The cord is 6 feet long. The majority of Hydor's products have a standard 6-foot cord.

Can the temperature be adjusted?
Answer by ChewyOct 20, 2017
The temperature can be adjusted.

What neater is best for a 5 gallon tank?
Answer by ChewyAug 25, 2018
The 25 Watt Aquarium Heater is ideal for 2 - 7 gallon aquariums.

Can this thermometer be used in a turtle aquarium?
Answer by ChewyAug 26, 2018
This heater is suitable in saltwater and freshwater tanks.

ReviewsWrite a Review

Rated 3.4062 out of 5 stars
32 Reviews
Would recommend to a friend

32 Customer Reviews

Filter by reviews that mention

Rated 2 out of 5 stars
By MissB 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 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 (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 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

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.

Rated 5 out of 5 stars
By AuntieM on Oct 22, 2018

Works perfectly

Keeps my betta’s 5-gallon Fluval tank at 78 degrees without the need for adjustment and fits inside the back compartment with the filter motor.

Rated 1 out of 5 stars
By danm21 on Aug 18, 2018

Bad quality

Went through 2 in about a year, they power on but around 6 months you will see burnt spots on heater glass and it won't heat the water anymore.

Rated 5 out of 5 stars
By Jemm on Apr 24, 2018

Perfect for bettas

It’s a great heater for small tanks, and the best part is that it’s adjustable which is hard to find in small heaters.

Rated 2 out of 5 stars
By Brewcity on Apr 14, 2018

Stopped Working

Got two of these the other day to replace the old ones I had(different brands) and suddenly they both stopped working. Both are in separate tanks and both tanks have dropped back down in temps...

Rated 1 out of 5 stars
By Dadams on Mar 22, 2018

Very Wrong

I had heater turned as low as possible and it still registers 86 degrees. 16 degree difference. If you love your fish please don't buy this heater. I switched to the tetra which has never let me down.

Rated 5 out of 5 stars
By bluestraycat on Feb 17, 2018

Aquarium heater

I bought two of the 25 watt heaters for my 3.5 gallon Betta tanks. It's difficult to find a good, adjustable heater for a small tank. It did take a couple days to get the water up to 80 degrees, but that's probably because I keep my home on the cool side (66-68 degrees) in the winter. I've only had the heaters a couple weeks, but I'm very happy with them. The only thing I would change is there is no indicator light to show when the heater is on.