Hydor Slim Heater Review

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One of the most popular, bar none, heaters that people look into buying for their betta fish is the Hydor Slim Heater made specifically for aquariums up to 10 gallons. Available in two different wattages, the 7.5 W and the 15 W, and two different shapes (oval and round), this heater is designed to keep your betta fishy happy and warm all year round in whatever size, shape and capacity up to 10 gallons his home is.

Now going into this, there is not really too much to say about this particular heater. It’s popularity speaks to its reliability and efficiency in maintaining the proper heat settings for your aquarium. This is mainly designed for betta tanks that are on the small side. Which is conveniently nice because most people have smaller size thanks for their betta fish. Now when we say “small” we mean down to the lowest of 2.5 gallons. If you have your betta fish anything smaller than that, we can only be friends if you promise to get a larger tank. Anyway, that has very little to do with this heater so, moving on…

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Whats In The Box!?
I’m going to make an assumption. I’m going to assume that you’re here reading about this aquarium heater because you care about your fish and know that bettas need to keep warm. You may not even have your fish yet and are currently in the process of setting up the aquarium of your dreams. Or your fishes dreams anyway. As was said before, this heater is mainly designed for heating smaller size tanks. We actually recommend that you consider getting this heater only if you have an aquarium that is up to 5 gallons in size. Anything larger than that, anything meaning your aquarium that is, and you want to look at different types of heaters. Not that this one’s bad, it’s just that there are other ones that you will be more happy with in the long run for heating larger size betta fish tanks.

A positive thermal coefficient, or PTC for short, is incorporated into the specially designed heating element that sets this under gravel aquarium heater apart from the rest. You can expect temperatures on of an average of 5 to 10° warmer than ambient room temperature when you utilize this heater in your aquarium. And I tell you the truth, this heater really does deliver on that by the way. Actually, over and over again I’m continually blown away by how well-made this tiny little heater is.

in general you can expect an increase of 5-7 degrees depending on aquarium size

As you can see in the picture, there are no glass components to this heater. Which is a very nice thing considering that this betta tank heater goes underneath the substrate in your aquarium.
This is a preset heater. Preset meaning that it is plug-and-play. Plug it into the outlet and it starts heating.The final temperature will ultimately depend on the existing ambient temperature of your betta’s aquarium before the heater is plugged in, but in general you can expect an increase of 5-7 degrees depending on aquarium size as well.
One thing about this heater that’s interesting is that it’s advertised as an under gravel heater, but you don’t actually need to use it that way if you don’t want. Now technically you don’t want your fish to come in direct contact with the heating pad, but it doesn’t have to be gravel that sits on top of this heater in your tank.

The Hydor Slim Betta Aquarium Heater itself is a good 3 inches long. Imagine if you will, a typical playing card. That is roughly the size and shape of the heating element. The part gets hot is very flat and very thin. If you want to affix the heater to the tank itself, it comes with a small piece of cabling that will assist you in that attachment. You want to make sure that you have a power outlet in your home that is no farther away than 5 feet from the end, or the hot part, of this heater. This is because the cord is about 5 feet long. And if you seriously must know, the power cord ends in a two-pronged receptor. This means that it is not a grounded connector.

How Warm Will The Hydor Heater Get?
To give you an idea about how high this will raise your aquarium’s temperature in general, in a 2 ½ to 3 gallon tank this will raise the heat a good 7°F higher than ambient temperature. Now don’t go quoting me on that exactly as your results may vary depending on what temperature you keep your own house at. My house is typically around 70 to 72°. That’s just to give you a rough ballpark idea.

Testing it out in a 10 gallon tank just for the heck of it, the water gets about 5° above ambient room temperature. Now in my situation where my house is heated to about 70 to 72°… That’s really not quite enough for me. But, if you live in a warmer house, maybe that’s all you need. Mind you that the 5° difference is for a 10 gallon tank and not a smaller size tank. In the above paragraph you’ll read that it raises the temperature up about 7° for a 3 gallon tank. I don’t mean to be redundant, I just want to make sure that’s clear.

As I said before, this heater for your aquarium is preset. That means it does not have a thermostat. Nothing to control the temperature to make it go up or down. When you have it plugged in it is on. When you have it unplugged it is off. This is not something to be concerned about as many many many aquarium heaters are designed this way and completely safe and, more or less, recommended over traditional heaters that have thermostats.

Please do not put this heater in an aquarium that is any smaller than 2.5 gallons. You may fry your fish.

This heater is safe for use in acrylic aquariums. This means that even if it is in direct contact with the acrylic floor of the aquarium nothing bad will happen. Well, saying things like nothing bad will happen kind of puts me in a liability risk so, I think it’s better to say nothing bad should happen in theory. In any case, this heater is designed to be used in acrylic tanks and glass tanks alike. Regardless of what the material is that makes up your betta tank, when using a heater of any type you should always check the heater periodically to make sure nothing strange is going on. That’s just common sense people!

Now, I have quite a few betta aquariums set up my house and, I really don’t use these particular heaters too very often in my setups. However, that does not stop me from having a drawer full (I have a lot of tanks) of these heaters. Why do I have a drawer full of these heaters? Because they are fantastic to use in a pinch. There are so many situations that can arrise. So many disasters that aren’t really disasters but, just situations where something goes wrong with one of the pre-existing heaters the another tank and you just need to turn up the heat in one of your those tanks. These are fantastic for those “in a pinch” situations. For me personally anyway.

The Hydor Slim Betta Aquarium Heaters are small and they’re easy to carry around with you. If you travel a lot or are still in school and going to and from your dorm room to your house. There’s a lot of off-the-wall situations were having a heater like this particular one comes in incredibly handy.

Uneducated Skeptics
One of the common complaints about this heater is that it is too large for some people’s aquariums. In fact if you going you look at some reviews on Amazon.com, many of the negative reviews are, in fact, negative for the sole reason that their heater did not fit inside of their aquarium. If you run into this problem… Get a bigger tank. I mean that both jokingly and in all seriousness. If this heater cannot fit in your tank, your tank is most likely far too small to raise a happy and healthy betta fish.

While I’m on the topic of complaints about this particular heater, another incredibly popular complaint is that it kills people’s fish. If you read the next sentence following that complaint in pretty much any of the reviews that are negative, you’ll see that the people were trying to heat aquariums that are sub 1 gallon in size. Please do not put this heater in an aquarium that is any smaller than 2.5 gallons. You may fry your fish. And as I said before, you really want to have your betta fish in an aquarium that is no smaller than 2 ½ gallons. If you want to read more on why this is, I’ve got an article betta fish bowls and vases that explains all about it. And I guarantee you it’s much more interesting than this review about a slim under gravel aquarium heater for your betta fish.
One of very side note, but still relating to this particular product, be careful when opening the packaging for this heater. Pretty much every package I’ve seen is so tightly compressed up against the heater itself that when you go to cut it open, you run the risk of slicing the heater itself. Now, that may be a frustration that I myself only have. But it’s one that I run into often with this heater. I don’t think I should be allowed to play with knives anyway.

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