Fish Tank Heater

I’d like to explain why heaters are necessary in the aquariums in this article. Before you continue reading, you must realise that some fish tanks don’t need any heating equipment, because they require other kind of conditions. But let’s go from the beginning.

First, make sure that your fish and plants need the same temperature. Naturally, it’s a bad idea to keep fish which prefer different temperatures. The same goes to plants. When you select the right fish species and the tank which should be large enough for all of them, you should choose the right accessories including heater for the tank. Generally, larger aquariums need more powerful heaters. The smallest aquariums on the market need only some 25 watt heater, but 300 L / 75 Gallon tanks require 300 or more watt heaters for sure. The size of a fish tank heater does matter and is also important from this point of view: Even a 50 watt heater can heat a 300 L aquarium, but the speed how the desired temperature is achieved is very questionable. Naturally, if your aquarium has a lid, then warming up goes very fast!

Some fish tank heaters may be integrated within filters, however in my experience this is not the best idea. It’s all because each accessory should be reachable in seconds. Additionally, sometimes you need to turn off the filter (when fish built a nest or laid eggs), but heater must be turned on. When you’re upgrading from small or old filter to a new one, you will also have to change the heater. Naturally, exceptions do exist.



Before you buy any such product, make sure you need it. Water heaters are needed especially during winter and other cold months when the temperature in a room is lower than 20°C (68°F). On the other hand, usually all fish species should survive temperature about 20°C because of a simple reason; water temperature in the wild usually varies from 18°C up to 30°C during 1 day! Bear in mind, that any creek or river is colder in the night and the temperature raises as the sun moves up in the skies. Of course, rooms usually offer stable conditions and very low temperature is very rare.

The second reason why you maybe need a warmer is that the fish you keep need high temperature for breeding purposes. Generally, most of tropical freshwater fish species will breed at about 27°C. In my experience, there are more important factors which will determine if any fish will breed. For example, stable chemistry, water current, pressure or so. All of my fish have bred successfully at 25°C.

Once you decide that you need some warmer in your aquarium, you should determine how powerful it should be. Well, I’m using 1x 50 watt aquarium heater in my 81 L / 21gal tank. To be honest, I must say that it takes longer until it raises the temperature to 28°C, but also I must say that I haven’t had any problems with it. It is capable to keep the water temperature at 30°C. In my opinion, an aquarist should use 1 watt for 1 L. So if you own a 200 L / 50 gal tank, use a 200 watt heater.

Don’t forget to place your heater at the place where the water current will flow to. This is usually somewhere nearby the filter and this place shouldn’t be overgrown with high plants. Also, the heater should be fully submersible and waterproof too. Spend more money on buying a quality heater, so you will not get up and find out that your fish are dead, because the heater immersed itself.

Just for make things clear, always use thermometer. You can also plug your heater into a timer, so it will create similar conditions like in the wild.

Important facts

Your heater must be placed in the aquarium! The size matters, and thus never put any big heater into fish tank that’s too small! Rather spend some time searching for a small heater instead of using a way too big one! It doesn’t look nice and it will waste a lot of space.

When you have a chance to choose from 2 or more aquarium heaters that are for sale, always compare their wattage, sizes, and warranty. If some heater generates 50W, it doesn’t mean that it requires 50W per hour! Output is always lower than power consumption!

Here, I provide some pictures of heaters, but I’m not trying to advertise any product. You can also find an example picture of how-to install a heating equipment into the fish tank here.


A heater in an aquarium


Sera heaters


Ferplast heaters


Stealth heaters

Image sources: victoria-adventure.org, aquariumsystems.com, practicalfishkeeping.co.uk.

Usual questions and answers

Start from beginning... "How do I use aquarium heater" and "How can I heat my fish tank?" should be answered before any heating equipment is bought. Usage is simple, heaters usually come with rubber suckers. You put the heater into the aquarium, attach it to the suckers that are attached to glass. Plug in to the electricity and it works! The second question and answer on it; Aquarium heater is just one option. Another is heating the room where you have aquarium or aquariums. If operating costs to heat your room are lower than electricity costs when using a heater, then it’s better to heat the room. It could sound weird, but if you have a fish house with, say, 5 or more fish tanks in just one room, then it’s worth a consideration at least. Leaving sunlight to enter the room via windows is another useful technique.

Many aquarists ask how to install a fish tank heater... It is necessary to follow all instructions given by the seller or given by enclosed guidelines that can be found in the heater package. Basically, if your fish tank heater is fully submersible, then you’re allowed to place it anyhow, but bear in mind that the water flow must reach the heater in order to distribute the heat. If your heater comes with thermostat, then make sure that you can easily modify desired temperature. Owners of submersible heaters don’t need to ask "How to install a submersible aquarium heater" as heaters usually come with things that allow one to attach heaters to glass. If you’re buying used heater, make sure that the package contains all equipment required for proper functionality.

Usual mistake of new buyers is that the size means power. In general bigger heaters produce more heat, but it’s not a must. Always check for wattage when asking "How big aquarium heater do I need?". Even small 200 W heater can be more effective than larger that generates less heat. Wattage is closely related to the question "How can I tell if my fish tank heater is working?" which is normal indeed! You should use aquarium thermometer along with any heater. Thermometers are cost effective solutions that usually don’t need any maintenance and give precise answer on question if your fish tank heater works or not. If you’re not sure, simply take the heater out of the aquarium, put it into a bucket with cold water and let it heat the water to 30°C for instance. Check the water after an hour or less depending on wattage of the heater. Also ensure that there is some flow in the bucket. There is a small red light on many heaters that simply say if heater heat or not. When you can see that red light, it means the heater heats. If it’s not turned on, the heater doesn’t heat (assume that your heater has a thermostat). If the water is too cold and if desired temperature that’s configured on heater is higher, and if heater doesn’ heat, it means it’s not working. Just to be 100% sure try the mentioned test with bucket.

After having a heater installed, some people worry about depth that’s good. The question "How deep should my aquarium heater go into the water?" has one simple answer; If the heater is fully submersible, then depth doesn’t matter. In most cases it can be placed horizontally as well as vertically or in any other direction. If the heater is not fully submersible, then you can find a red line (or black, the colour may differ) on the heater - this indicates the maximum immersion. Also there should be another line informing about minimum immersion.

"What fish don’t need a heater?" is another question that’s asked by newbie fishkeepers a lot. It’s necessary to understand that if you’re able to offer your fish a temperature of 22°C each day a year without any heater, then most likely you won’t need a heater at all. In some cases heaters are good; during curing diseases for example. You could have been told that many tropical species require a temperature of 25 or 26°C at least, but one must understand that temperature in nature changes during the day. It’s not unusual that during nights, temperatures of water in lakes or rivers are lower by 5-10°C in comparison to noons or afternoons. However, we can 100% say that coldwater species don’t need a heater at all! Naturally, they need chiller instead.

Unlike the previous question, many people also ask "What fish can go into a room temperature tank?". All tropical freshwater fish as long as the temperature varies between 20°C and 30°C during the year.

If you’re buying a fish tank heater without thermostat, it may occur that the water is overheated. So the question "Heater overheated my tank, what should I do?" must be answered too. The solution is very simple; Once you noticed that the water is too hot, do a partial water change. If you don’t have any chlorine remover, then don’t hesitate to use tap water as high temperature may be a worse enemy than chlorine. Firstly change 10% of water, this depends on capacity of the aquarium. If it’s small, a small water change will help. If the tank is big, then it will be necessary to perform more partial water changes. If there is a lid on your aquarium, remove it until temperature becomes stable and lower.

The problem of overheating is related to wattage. Not every aquarist understands what is wattage and thus they ask "What is the wattage of a fish tank heater?". The answer is simple, wattage means input. In general we can say that the higher input, the higher output. A 200 W heater will heat a 100 liters aquarium much faster than a 50 W heater. Use our calculator, enter your fish tank’s dimensions and see what’s recommended wattage for your aquarium. "What if I buy a larger aquarium heater than I need?" is what people ask too. While buying all accessories they’re not sure, or simply the shop assistant convinced buyers to buy bigger, better, more powerful one. The answer is as simple as possible; It’s not a problem. As long as your aquarium can be heated properly, the size or wattage don’t matter.

"What brand of heater is good for fish tank?" is one of the most important questions asked by buyers. I use heaters by Sicce. But it’s not the only brand and you should consider all of them. Buy one that includes thermostat for sure. How much are fish heaters? This depends on wattage (higher wattage = higher price), but in general we can say that good heaters start at $40.

Additional questions and answers about heaters

On March 17th 2011 this page has been updated once again; Questions and answers from Aqua-Fish.Net/Answers were merged with this article. Some of the questions below may be answered already on this page, however it’s easy to find "your question" below; Instead of searching for answer within the article and comments that can be found below sponsored links. You’re welcome to ask your questions if they haven’t been answered on this page yet! Simply use the form that can be found at the bottom of this page.

• Which heater is recommended for my fish tank?
  Answer: This completely depends on how big is your aquarium. Let’s mention a few examples:
  
  * Dimensions are 52x55x100 (cm; height x width x length), then you need heaters which give output of 353W.
  * Dimensions are 40x40x60 (cm; height x width x length), then you need heaters which give output of 118W.
  
  You can calculate these numbers easily with our calculator.
• What heater should I use for a 75 gallon aquarium?
  Answer: You can use one or more heaters, their total wattage should be approximately 350W. Naturally, if the room temperature is 24°C during the year, then you can use lower wattage heaters too.
• Why is my goldfish aquarium warm?
  Answer: Goldfish do not require heaters in the aquarium, if there is one there remove it. The only other reason is that the aquarium is absorbing heat from the external room temperatures.
• What types of fish don’t need heaters?
  Answer: Coldwater fish such as koi and goldfish do not require the use of a heater unless temperatures drop below 52°F (11 °C).
• How can I tell if my heater is working?
  Answer: Most aquarium heaters are now fitted with a led light that tells you when they are on or off. A good thermometer will tell you if the correct temp is being kept by the heater, If the temp rises too high then the thermostat may be broken, likewise if the temp starts to drop over a period of time the chances are that the heater has failed.
• What should my thermostat be set at?
  Answer: Most fish like their own temperature range and therefore should be kept only with others that both will live peacefully together and can tolerate the same water conditions. The store that you purchased your fish from will be able to give you the temperature to keep your fish at or you can research your fish online or at your local library. Some hobbyist raise the temperature of their aquarium by a degree or two in an effort to treat a parasite infection that depends on water temperature for its life cycle; most commonly ick.
  
  Feel free to browse our fish database (see fish images and profiles at the left side of this page) to find what temperature is preferred by your fish.

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