The Aquarium Heater Guide For Betta Fish

the aquarium heater guide for betta fish
Do betta fish need a heater? Yes, yes they do. Getting an aquarium heater for your betta fish sounds like a pretty straight forward issue to get past. That is, until you see how many there are available in all of their various shapes, sizes and… wattages. If you are new to the world of aquarium heaters, your initial confidence can quickly go from “I know how to buy a heat thing for my fish” to “Yeah, I need help plz”. And ‘help’ is the main point of this splendiferous (albeit slightly un-exciting) guide to aquarium heaters!In days gone by, heating your aquarium meant purchasing one of only two available types of heating devices. That would be the one-setting-only, thermostatic submersible type that were exclusively made out of glass, or those “automatic” heaters that you would hang on the back of the aquarium. Now days the arrangement and assortment of available heaters for your hobby fish tank can fill entire aisles of the pet stores you shop in. You can select from ranges of size and shape, varying temperature outputs, the materials the heaters themselves are made out of, wattage ranges, incremental control systems, and the list of options keeps growing as time moves on.All in all, it’s actually not really that hard to make a smart decision on which heater to choose for your fishtank setup. I’d say that first and foremost, learning the following rule of thumb will help you get 90% of the way to finding your perfect aquarium heater.

25 watts of power for every 10 degrees of existing ambient temperature for every 10 gallons you need to heat.

So, and example of this aquarium heater guideline would be: Say the ambient temperature of your home is 70°F. You have a 10 gallon aquarium that you need to be heated to 78°F. For a single setting heater, you would need 25 watts of power to get that 8°F difference. However, if you were to get a 50 watt tank heater with variable temperature controls, you would most likely be better off as you could set that heater to the low side of the power draw and have room to increase if the ambient temperature of your home gets colder.

For many people, a fairly large concern is that their lack of knowledge going into purchasing a heater for their betta fish tank will lead to a very bad outcome. For the most part, aquarium heater issues arise when the heater being used isn’t the correct wattage for the capacity of the aquarium it’s being used in. Basically this means that betta owners will experience a very quick temperature rise in their tanks that doesn’t seem to stop. Remembering that rule of thumb above about tank heater wattages and aquarium capacities will help ensure that you end up with healthy and happy betta fish as opposed to crunchy betta fishsticks.

That quoted rule of thumb above is something that has worked and worked very well for me over the past who knows how many years. I say that because I have often found that the information you are given by a salesman in a pet store is often quite different than what I’ve writing here in this guide to aquarium heaters. While I’m not saying the the typical schoolyard “I’m right and your wrong” kind of thing, I just want you to keep aware of possible differences of information you may be given. Often times the products retail salesmen will suggest are quite a bit higher in wattage and quantity than you really need. I’ll let you draw your own conclusions as to why that may be.

When you do finally make your aquarium heating selection, and regardless of type, you need to set it up in a way that there is good circulation around the heating element. Aside from safety concerns to the aquarium and the fish living in the heated tank, providing a good amount of circulation around the aquarium heater will make it much easier to control the temperature. Good water circulation around the heater also makes the heater’s readings far more accurate.

read the manufacturer’s boring directions thoroughly!

There is a type of external aquarium heater called an in-line heater that seems to be a work-around to the water circulation problem common to many fishtank heaters. In-line heaters heat the water outside of the tank first and then passes the heated water into the aquarium. These in-line aquarium heaters can be pretty tricky to set up properly and, at least in my experience, do not seem to do a very good job of evenly heating the aquarium. While I don’t want to discourage you from trying things new things on your own, all I can give is my own cumulative years’ experience with these things. More often than not, these in-line heaters will burn out, and over heat the aquarium as they do. Like I said before, just because I got “burned” on a particular type of product doesn’t mean that you will.

One other thing to mention is that if you have a larger size aquarium and the temperature of your home is 25°+ degrees colder than you want your aquarium heated to, you can install a second heater following the same guidelines as stated above. For larger sized fish tanks, doubling up on your heaters rather than purchasing one very strong heater will let your aquarium distribute heat more efficiently.

Keep in mind that many heaters are specifically designed to heat only up to a certain high temperature. If you try and heat above the recommended high temperature setting, you may end up having to buy a new heater in short order. Heater failure, damage to the aquarium and injury to the fish its heating may occur if you don’t carefully follow the guidelines for the specific heater you are using. So, read the manufacturer’s boring directions thoroughly!

(This video is a bit long, but it is filled with awesome betta aquarium heating tips!)

Basic aquarium heater setup

First and foremost, when you go to install the new aquarium heater (any aquarium heater), you should place the device into the aquarium water without having the heater plugged in, for at least a half hour. Letting the heater soak in the fish tank while it’s un-powered will allow the device to acclimate all of its internal components to the initial temperature of the aquarium. By doing this, you are trying to avoid heater failure and damage.

With submersible heaters that are the pre-set type, you are going to want to make sure that you submerse the heater to at least the minimum water line. When adjusting the temperature control dial on models that are temperature incremental, the adjustments should be made in small quarter turns. If you can, smaller turns than even that on the dial are better. Automatic heaters do not, of course, have the ability to adjust the temperature setting manually like this.

it is generally recommended that you do not adjust the temperature on the heaters dial more than 5°F per day

Aquarium heaters that are the “hang on the back” type should be submersed exactly to the water line indicated on the device. You want to pay careful attention to the water level on these types of heaters because if the water line is either too high or too low, heater failure can occur. Generally speaking, it’s not hard at all to maintain the proper level of submersion with these types of heater. Water evaporation can cause the water line to lower over time, but you will be checking on your tank more often than not like a good betta owner… right?

With fish tank heaters that have digital controls, it is generally recommended that you do not adjust the temperature on the heaters dial more than 5°F per day. That is, if you are adjusting the temperature of the tank while your fish are living in the aquarium. If the tank is void of aquatic life, changing the temperature incrementally as recommended above doesn’t really matter.

Specifically with the pre-set types of heaters, you should do a few water temperature tests to make sure that the real reading are what the heater itself is set to. It’s pretty common to have the real temperature of the tank be off by a few degrees Fahrenheit with pre-sets. You could have your pre-set tank heater at 78° and come to find out much later on that the real temperature in the tank is 75°. While this doesn’t sound like too big of a difference in temperature, to a betta fish, it is.

If you are one of those lucky people that have similarly lucky betta fish swimming in a really large tank and are subsequently using more than one heater, adjusting each heater individually over the course of a few days is recommended before you run both heaters at the same time. It can sometimes be difficult to set a correct temperature for an individual heater while there is another heater currently running in the tank. That advice does kind of get thrown out the window if you are running two heaters because the combined wattage is what you need to properly heat your aquarium. In that case, you are going to have to try and set both at the same time, making micro adjustments to both to get that perfect temperature. This can take some time as you will be in a sort of temperature war with the heater you are not fidgeting with. Not to mention that heaters are often “off” by a few degrees that they say they are at, so using their temperature reading gets confusing and offers little help.

Just in case you see this happening and start to worry after you set up a glass heater, it’s fairly common to have a small amount of condensation gather on the inside of the heating enclosure. This is not necessarily a sign that your new quartz aquarium heater is leaking and defective. If you notice that the condensation is growing and pooling a good amount inside the bottom of the glass enclosure, you may have a problem. A little condensation on the inside of these glass heaters is a relatively normal occurrence though.

Water and electricity don’t mix

Please make sure that you employ a drip-catch when connecting the heater to a power supply.

Please make sure that you employ a drip-catch when connecting the heater to a power supply. This is not a difficult thing to do and doesn’t cost anything. Imagine a stream of water traveling down the heater’s power cord to the power outlet. If the cord is running in a straight line at a downward angle to the outlet, water will enter the outlet. You do not want this. To stop this from happening, make sure that there is enough slack in the heater’s power cord to fall just below the power outlet, and then rise up again to attach to the outlet. Imagine a “U” shaped bend in the power cord, caused by gravity, that falls below the power outlet before being connected to the outlet. This U shaped bend in the power cord will be the lowest point that the water can travel down the cord. As water cannot travel on its own at an upward angle, the “U” shaped bend will keep any water traveling down the power cord from entering the power outlet.

I do not want to recommend the use of power strips for use with aquarium heaters. Although I myself may or may not use them for my own heaters, most (if not all) aquarium heater manufactures warn against the use of power strips. I am sure this is for a good reason… that I may or may not listen to myself. In any case, if you were to go against my non-recommendation of using power strips, make sure that you set them up in a way that you can use that “U” shaped bend in the power line as described above. Power strips are commonly placed at the lowest point in a house, the floor. That would not be a good place for power strips to be as you could not use a “U” bend to catch any water before it hits the power outlet.

The power cords for aquarium heaters are specially designed and manufactured for use with those heater. Using an extension cord may not be the wisest idea. The power draw from the heater may cause inferior extension cords to heat up causing the cord’s insulation to fail. If you decide to go against this warning, at the very least, make sure that the extension cord is not coiled at any point. Coiling can increase the rate at which the extension cord heats up, and therefor increase the danger in its use. Please be careful with their use. If in doubt, don’t use them.

bettafishy viaaqua 50 watt quartz glass submersible heater

Preset aquarium heaters

you really want to give these heaters a good 30 minutes of pre-soak time in the fish tank before you even plug them in.

Preset aquarium heaters (also called Thermostatic heaters)is a type of aquarium heater that has an analog thermostat built into the device. Some types of preset heaters actually have a remote sensor that gauges the aquarium’s temperature separately from the main heating unit itself.

There is a huge assortment of makes models and brands to choose from when shopping for a preset heater. Many of the models available today have really nifty temperature gauges built right into the side of the device as well as a temperature control dial that allows you to set the temperature of the aquarium to fairly exact parameters.

Pretty much every thermostatic heater you can find is fully submersible. These submersible heaters all come with a line of some sort that indicates the minimum submersion depth needed to function without fail. You need to keep an eye on the water level meeting that minimum submersion depth so as not to cause the heater to fail. In general, this is about an inch to an inch and a half from the top of the heater. In most cases you will not have to or want to fully submerge your preset aquarium heater. There is also some chatter about these preset glass or quartz heaters not actually being fully submersible. I have yet to find and test one that isn’t.

As was mentioned earlier, you really want to give these heaters a good 30 minutes of pre-soak time in the fish tank before you even plug them in. This will give the aquarium heating unit some time to acclimate its internal components to the existing temperature of the aquarium.

When you do go to plug in and turn on the preset heater, you should really have a secondary thermometer on hand. While the temperature gauge built into most of these heaters work fairly accurately, it’s good to have that second thermometer to verify that the temperature is actually what the heater says it is. When making adjustments to the temperature of the aquarium, please make the changes in small increments rather than all at once. Also note that the settings on the knob should be used as only a rough guide to show you in which direction the heater is being adjusted. You shouldn’t always trust what is factory imprinted on the control knob as being what the temperature will end up as.

Years of experience shows that its normal for preset heaters to be off by a few degrees right out of the box. After getting a reading off of your secondary thermometer, try to remember the variance in temperature for later use in making adjustments. If one of my aquarium’s heater dial is set to 78°, I know that in reality it is closer to 80° just from experience and the use of a separate thermometer.

When it’s time to change out the water in the betta tank, you should remember to turn off any heater as well. You really don’t want to expose the heating element or the heat sensor to air. This may not break the unit all at once if you do by mistake, but it can, and probably will, shorten the life of the heater. It’s also a good idea to let the heater sit while turned off and still submerged in water for around 20 minutes before the actual water change. This will give the heater some time to cool off and let the temperatures of both the water in the tank and the heater equalize.

Years of experience shows that its normal for preset heaters to be off by a few degrees right out of the box.

When mounting the preset heater to the betta’s aquarium you should preferably mount it vertically. This means straight up and down relative to the tank. While this may seem as a no-brainer, some people do choose to mount their heaters horizontally, or even at a diagonal. If you read the instructions (as you should) given by the heater’s manufacturer, you will see it written that you should only ever mount the heater in a vertical fashion. There is some worry about water breaching the seal at the top of the heater and causing failure of the device as well as damage to the aquarium and the home the tank is sitting in. As I said before, many people disregard this warning and mount their heater in whatever direction they want. I think I’ll just leave it by saying that you are going against the “rules” by mounting the heater in any direction other than vertical.

In case you wanted to know how these preset heaters usually work, get ready to read some nerdy stuff. These types of aquarium heaters often use a thermostat that keeps an eye on the impedance of a resistor that is used to accurately measure temperature differentials and changes in an aquarium. This resistor is called a thermistor. Some preset heating devices detect temperature changes by measuring the electric potential difference across a thermocouple.

If you were to purchase 10 different brands and models of preset heaters, there is a fairly good chance that you would notice some temperature reading differences between them. Not generally to a great degree, but differences none the less. This thing that you would certainly notice as a difference between them would be things like price and quality. Long term reliability between different makes and models of preset heaters would also be something that you would notice given enough time.

In all of my many, many years using devices like these, the one thing that  seems to happen the most when these preset heaters start to fail is that the difference between the temperature given and the actual temperature of the tank grows larger. This is, of course, after the heaters have been in use for quite some time. Nothing lasts forever. In any case, there doesn’t seem to be much difference in overall temperature reading reliability between the name brand and the aftermarket models.

You will probably not have to ever return an aquarium heater, but in the event you end up having to, you should take a look at the return policies on the particular make and model you decide to purchase. Some brands of aquarium heaters are actually pretty difficult to return. When I speak about the return process as difficult, I am not saying that they can be impossible, but rather that they give specific instructions to return products directly to the manufacturer as opposed to the retail outlet that you purchased the device from. Maybe that isn’t a big deal to you, but I don’t like jumping through that hoop. As I said before though, you will most likely not have to return a heater because is defective out of the box.

bettafishy elite thermostatic heater

Hang On The Back Aquarium Heaters

If you have one of these types of heaters, it is more than important that you make sure that the water level is maintained at the required level indicated on the heater.

“Hang on the back” heaters are also known as “Automatic” and/or “Non-Preset” aquarium heaters. As the first of their many names implies, they are designed to “hang on the back” of the aquarium you are trying to heat. Go figure huh? Their other commonly known names (such as Automatic) are a bit misleading however, as they do not adjust their power output by sensing the current temperature.

They work through what is known as a Remedial thermostat. When you make adjustments to the control dial on this type of heater, you would be either tightening or loosening metal contacts on a bi-metal lead. When you go to tighten the contacts, or basically turn up the heat, all the heater does is turn “on” for a longer duration of time. Turning down the dial makes the heater turn “on” for a shorter amount of time.

If you have one of these types of heaters, it is more than important that you make sure that the water level is maintained at the required level indicated on the heater. Failure to maintain the proper water level can and will end up causing the HOB heater to fail. Failure for these types of heaters generally means that the heater cracks under stress of dry heat. This is really not a good thing when you have it still plugged into an outlet and partially submerged still the aquarium.

On the plus side of things with these types of heaters, they are almost always very affordable. Also, because the literally hang on the back of the tank, they will fit most any aquarium. Because of their affordability and easy use in virtually any tank, many people keep one or two of these heaters in a drawer to be used in case their primary aquarium heater fails. I myself have one tucked away in a drawer… somewhere.

One thing you have to make sure to remember with these heaters is that if you live in an area with wide ambient temperature swings, be sure to keep a close eye on the temp of the tank. Mind you, these hang on the back heaters do not adjust themselves based on the temperature of the aquarium, but rather as a kitchen timer would, turning on and off when the “clock” winds down. If the temperature outside today is 10 degrees hotter than yesterday, the temperature of the tank with one of these installed will be hotter than it was yesterday. Even if you don’t live in an area with wide temperature swings day to day, remember to check the heater’s setting at the very least seasonally. I’m sure you have at least 2 definable seasons where ever you are reading this from.

As with any heater that you submerge into water, please let this sit in the aquarium water while unplugged from the outlet for about a half an hour before you turn it on. Just like the the other heaters, you want to give the hang on the back heater some time to acclimate to the ambient temperature of the aquarium water. If you forget to do so, you might have to take another trip to the store to purchase another. You might not also, but why risk it?

bettafishy aqueon preset heater

Plastic covered or resin heaters

Next on this list of aquarium heaters is the plastic or resin covered type of heater. You can consider this a closely related type of heater to the glass/quartz preset heater described above. Some refer to these heaters simply as “smart” heaters. They generally have a low temperature variance and built in LED warning system. The warning system on these types of devices generally kicks in when the temperature of the tank is +/- 5°F from whatever temperature you set the device at.

bettafishy aquatop nano aquarium digital heater with led d1ht

Digital Heaters

These heaters are also closely related to the preset heaters as described above. They are actually almost completely the same in general except for the fancy digital temperature readout display built into them. Well, actually the temperature control circuitry is a bit more advanced than the typical preset heater provides.

Some of the reasons you may want to consider this type of heating system over the typical preset heater are:

●    They provide a dry detection auto-shutoff
●    Higher accuracy temperature control
●    Big and bright temperature display
●    2x insulation surrounding the heating element

bettafishy hydor slim heater for bettas

Under Gravel Aquarium Heaters

Each device has its own temperature standards and variances, but as a standard, most will increase the temperature of an aquarium by around 5 degrees of the ambient temperature.

These types of aquarium heaters are really popular with new betta owners. These “under the gravel” tank heaters are made specifically with small capacity aquariums in mind. Most of these mini heaters are heating rated up to about 5 gallons. That is to say, if you have an aquarium that is 5 gallons, you might be better off looking at a “real” in-tank heater like a preset or HOB heater. In any case, these little tank heaters do work and you should know they exist.

As the name implies, these heaters are meant for use underneath the aquarium’s substrate. This also does mean that these devices are fully submersible. Because they are meant to be used under the tanks gravel, one kind of neat thing is that they are practically invisible. Nothing hanging on the wall or over the side of the tank. That is, minus the water-proof power cord. Aside from that though, they are clean looking.

These types of heaters are always on. There is no control dial with these that allows for temperature adjustment. They work on a sort of internal “automatic” setting that adjusts the temperature of the aquarium based on a hard -set internal temperature limit. You could look at this as a “set it and forget it” nice thing, or as something that will cause you excess trouble by constantly having to monitor the temperature of the tank. Each device has its own temperature standards and variances, but as a standard, most will increase the temperature of an aquarium by around 5 degrees of the ambient temperature. Because most homes are heated to around 72°F, this 5 degree rise will get the temperature in the tank just inside the preferred range for a betta fish.

It is very, very hard to give your betta a consistent aquarium temperature inside of a small capacity tank. The larger the tank, the more easily you will find it to be keeping the tank set where you want it. While these under the gravel tank heaters are better than nothing at heating up a small tank, you will find that you end up with a happier fish if you opt for a larger, 5+ gallon aquarium with a “real” heater.

bettafishy hydor in line external heater original eth

In-Line aquarium heaters

These types of heaters are can be nice to have in certain situations. Especially when you have a very large tank.

These types of heaters are can be nice to have in certain situations. Especially when you have a very large tank. Most betta fish owners, by a very large margin, will not have their bettas swimming in 50+ gallon tanks and can probably skip reading about these. I’m including their description in here anyway because this guide is about aquarium heaters, and this type is one.

This type of heater seems to bounce back and forth in popularity over the past many years. There was one type if in-line heater where you would place your normal submersible heater into a special casing to basically convert it for use as an in-line heater. That was kind of a cool design in theory and it inspired many to make do-it-yourself versions. I’m not recommending you try that if you are so new to this that you are only hearing about in-line heaters for the first time.

Then of course there is stand-alone type of inline heater such as the Hydor In-Line External Heater. That particular make and model of inline heater has been around for quite a while and has gained a great reputation for working well and being reliable. Most people actually picture this particular heater in their mind when talking about inline heaters.

One last subtype of inline aquarium heaters is the slightly lesser known canister type. If you are familiar with canister filters for your tank, these heaters work in a similar way with the exception that you place your heating element into the canister ports instead of a filter.

In general, out of purely personal experience and therefore admittedly a one-sided opinion, I have not found in-line heaters of really any type to be particularly good at accurately and evenly distributing heat in the aquarium. Failure rates of the inline devices were always much higher than that of other forms of aquarium heaters as well. That being said, if you do find yourself fortunate enough to own a very large aquarium, and do not mind perfect heating accuracy, these types of heaters are fairly bargain priced as compared to buying multiple heaters that are submersible. I see it as a sort of trade-off with price and functionality.


There’s a lot of information in this article. Much of it you probably don’t need to have to know in order to choose, keep and maintain the correct temperature and overall environment for a happy and healthy betta fish. Bettafishy figure it’s always good to know what your options are just in case you find that your current heating setup isn’t cutting the mustard for you or your finned friend.

All in all, you need to take into consideration only a few different things before making that final decision of which heater to choose.

●    The size of your tank
●    The fish you choose to keep
●    Regular outside temperature fluctuations
●    Temperature sensitivity
●    And your budget

In most cases, choosing a typical preset heater for a 10 gallon tank will suit your betta just fine. Taking a look at the under-the-gravel heating options would be wise for tanks in the 2.5 gallon range. You probably want to veer away from those in-line heating options unless you have a very large tank. Don’t forget to re-read that handy Rule Of Thumb about choosing the correct wattage that’s near the beginning of this article. Whatever heater you end up with, don’t forget that the whole point of picking out an aquarium heater is so that your betta can swim in water that is as near to that 78°F-80°F range as possible. And lastly, you might consider picking up one of those Hang-On-The-Back heaters for use as a backup source of heat should something go wrong unexpectedly.


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