The Importance of Marine Aquarium Heaters

Welcome to Simple Reefs. We are a brand new website designed to take the stress and expense out of starting your very own marine aquarium. With us being a brand new website, we have been looking at some of the basics of Marine Aquarium ownership. That brings us to the subject of aquarium heaters. Today, we are going to be looking at the importance of marine aquarium heaters and how they work.

Aquarium Heaters and Maintaining Thermal Stability

When you are jotting down your list of must haves for your new marine aquarium, a heater is probably near the bottom of the list. Sure, you might recognise that you need a heater but they aren’t a particularly interesting piece of equipment.

When you have fancy lights to choose, livestock to plan for, a rock scape to construct, and a clean-up crew to buy, a heater seems quite boring. After all, there isn’t much fancy about them. They are simply there to heat up your water. The truth, however, is a bit more complicated than that.

The role of the humble heater in your marine aquarium is, often, a little misunderstood. Sure, they are there to heat up your water but their role is much more important than that. They are absolutely crucial to maintaining thermal stability.

Don’t get me wrong, I am not trying to pull the wool over your eyes, here. Thermal stability is just a fancy way of saying “maintaining temperature” but the term becomes a lot more significant when you consider the context. The creatures in your marine aquarium, for the most part, come from tropical locations that are fairly warm and very stable.

When we say tropical, we basically mean that the temperatures that they would live in would range between 24°C and 28°C (75°F to 82°F). That specific temperature is, obviously, important but what is even more crucial is the lack of variation in that temperature. After all, the temperature of the sea where these creatures are originally from wouldn’t fluctuate a great deal.

The Impact of Thermal Stress

The sheer enormity of the sea acts as a thermal buffer which protects from temperature swings. This means that the coral, invertebrates, and fish in your aquarium simply aren’t adapted to tolerating temperature fluctuations. It shouldn’t, in theory, happen all that often in the wild so they haven’t needed to evolve to cope with it.

This is, actually, one of the big concerns with global warming. If temperatures drop or increase, we are going to see a less healthy fish population and mass levels of coral bleaching. In fact, it is happening right now and on a very concerning scale. An increase in sea temperature has caused a mass bleaching event all over the world due to thermal stress. Thermal stress is, for lack of a better term, heat induced bleaching.

When we build our own marine aquarium or reef, we are, basically, attempting to recreate a piece of the ocean. With this in mind, it is massively important to recreate the conditions you would find in the sea as closely as possible. This means stable temperatures between 24°C and 28°C (75°F to 82°F) with limited fluctuations to prevent thermal stress.

Temperature Fluctuations Cause Big Problems

Since the creatures in your aquarium haven’t actually evolved to tolerate temperature swings. You can start to see a number of problems when your temperature isn’t stable. Naturally, these symptoms vary depending on whether your aquarium is too hot or too cold but they all bear mention.

Stress and Weakened Immune Systems: You know what it feels like to be too warm or too cold. You feel more stressed and less capable of functioning. Marine life under thermal stress does the same. They become more susceptible to diseases; their immune systems are compromised, making them vulnerable to bacterial infections, parasites, and viral outbreaks.

Issues with Metabolism: Every biological process within a marine organism, from digestion to respiration and reproduction, is dependent on the temperature of the water. Temperatures outside the optimal range can slow down or speed up metabolic rates. This can lead to inefficient nutrient absorption, stress, stunted growth, and organ damage.

Coral Bleaching: For reef aquariums, temperature stability is paramount. This is even more significant with delicate coral like SPS. Even slight, prolonged temperature increases can cause corals to expel their symbiotic algae (zooxanthellae), leading to coral bleaching. Coral can, sometimes, recover from bleaching events but this is fairly rare. Bleaching is often fatal.

Behavioural Changes: When temperatures are outside of their natural range, fish may become lethargic, lose their appetite, or exhibit bizarre swimming patterns. Invertebrates may retract or become inactive. Your coral may refuse to come out and you may even notice more fish aggression.

Reduced Oxygen Levels: Warmer water holds less dissolved oxygen than cooler water. While this isn’t a huge concern in aquariums with protein skimmers and decent aeration from surface agitation. Excessively high temperatures can exacerbate oxygen deficiencies, especially if coupled with high bio-loads.

When you think about an aquarium heater as a way to prevent these issues, it suddenly seems a bit more interesting and a lot more vital.

The Role An Aquarium Heater Plays and How Heaters Work

An aquarium heater is going to take the water in your tank, heat it up to the desired temperature, and then it is going to keep it there. It does this by measuring the current temperature of your water, switching on when the water is too cold, heating the water to the pre-set temperature, and then switching off.

As the water in your tank starts to cool, it will switch back on again, repeating the process. This will allow your water to be maintained at a stable level with minimal fluctuations. But this conjures up a question – what are the separate parts of an aquarium heater? Let’s take a look.

1. The Heating Element

The meat and potatoes part of your heater is the resistive heating element. This is usually a coiled wire, often nichrome, encased within a waterproof tube. This tube is most commonly made of glass, but more expensive options are made of titanium. When electricity flows through this wire, it encounters resistance. This resistance creates heat which is then emitted from the coil, warming up the water around it. This is the same basic idea as you would find with toasters, electric kettles, and other heating appliances.

A marine aquarium heater, at its core, is a relatively simple device designed to maintain a consistent water temperature, crucial for the well-being of its inhabitants. While there are a few variations (like external or titanium heaters with separate controllers), the most common type for home aquariums is the submersible, thermostatically controlled heater.

2. The Thermostat

The thermostat is the part of the aquarium heater which makes the device automatic and completely hands-off. The thermostat monitors the water temperature around it. When the temperature drops beyond a certain, pre-designated, point, it switches the heating element on. When the temperature reaches the set value, it turns the heating element off.

There are two main types of thermostats commonly found in aquarium heaters. We have the old fashioned Bimetallic strip type and the more recent electronic thermostat.

The Bimetallic strip style thermostat is the kind you are going to find in those basic, affordable, glass heaters and older heaters. A bimetallic strip consists of two different metals which are bonded together. The metals expand and contract at different temperatures.

When the water is cooler than the set temperature, the strip bends and completes an electrical circuit which, in turn, activates the heating element. When the temperature warms up, the strip begins to straighten out which, obviously, breaks the electrical circuit, deactivating the heating element.

This is a devilishly simple way of controlling temperature and quite affordable, too. The downside is that it is less precise so expect cheaper aquarium heaters to be a little on the inaccurate side of life.

Electronic thermostats can be found in higher cost and more modern aquarium heaters. These use electronic sensors, such as thermistors, to measure the temperature of the water. You will set the temperature on the device beforehand and the device will constantly compare the water’s current temperature to this setting.

When the temperature drops below this, the thermostat will activate the heating element. When the thermostat detects that the temperature is back to the pre-set level, it will deactivate the heating element. It’s the same principle as the bimetallic strip, just a lot more accurate.

External Thermostats work on a similar principle. They usually consist of a digital display which you will keep outside of the water, a plug socket to plug your heater into, and a temperature probe. You set your desired temperature on the display and can, often, set a range of fluctuation that you are comfortable with (i.e. 1-2°C).

The probe will sit in the water and constantly monitor the water’s current temperature. When the temperature slips outside of your set range, the device will send power to your heater which will switch on and begin warming the water. When the probe detects that the temperature is back in range, the device will stop providing power to the heater.

Most external thermostats require you to actually buy a heater to use with them. They don’t always come with one included. The benefit of that is the fact that you can couple the thermostat with a high quality, more efficient, and almost indestructible, heater like a titanium heater for more stability and security. External thermostats offer a lot more customisation and flexibility, as well.

Some external thermostats even provide an option for cooling your water. These will include an extra plug socket for a fan which sits over the top of your water. When the thermostat detects that the temperature has climbed beyond a certain point, the fan will be switched on to cool the water.

More Advanced Thermostats are available and tend to come in the form of probes for tank automation systems. Automation systems are designed to, basically, manage numerous different aspects of your aquarium. They can be built to measure pH, measure temperature, control lights, control flow, dose elements, top up water, and even change water.

While the probes can be cheap and accurate, the automation systems are expensive. They work in the same way as external thermostats. The probe measures the temperature and, when the temperature drops, sends a signal to the automation device to turn on the heater.

I know for a fact, however, that there are going to be people reading this and thinking “My house is always warm, I don’t need a heater”. Let me tell you why you still need to use an aquarium heater.

3. Indicator Light

You want to be able to tell the heater is on, right? The indicator light is there to do just that. When it is lit up, the heater is actively warming the water. Some heaters come with digital displays to relate whether the heater is active and to even communicate problems. It should be noted that many heaters designed to use with external control devices will not have an indicator light. My titanium heater, for example, does not have one.

4. Waterproof Casing

This is, quite simply, the exterior casing of the heater designed to transfer the heat from the heater element without letting water into the device. These can be made of glass, titanium, and sometimes even plastic. Glass can be prone to breaking which can be catastrophic to your tank. Still, it remains the most common kind of aquarium heater because it is the most affordable.

5. Plastic Guard

Not all aquarium heaters will have this but it is a very useful addition to glass heaters. A plastic guard will fit around the heater itself. It will allow water in so that it can be heated but will prevent fish from touching the glass and burning themselves. It may also help to prevent, or minimise, a catastrophic explosion. Plastic guards can usually be purchased separately if your heater doesn’t come with one.

6. A Mount

This is another obvious one, most heaters will come with a way to mount it to your glass. These usually consist of suction cups and plastic clips which will mean you need to clean the glass before mounting. They are a bit hit or miss and can slide off but they are very much the standard for aquarium heaters.

Things to Keep In Mind

There are a few important things to keep in mind when it comes to aquarium heaters. The first is the fact that they vary greatly in wattage and there is a good reason for that. When we talk about wattage, we are referring to the amount of electricity they use. More electricity can produce more resistance which equates to more heat.

If you have a large aquarium or the ambient temperature of your home is lower, you will need to invest in a higher wattage aquarium heater. The more water there is or the more the water needs to be heated, the more power it will take to produce the necessary heat.

You need to make the calculation for aquarium heater size based on the coldest temperature that your room is likely to be at. It is probably best to work this out considering how warm your room will be in the dead of night. That will provide you with plenty of redundancy if the room temperature drops significantly in the early morning hours.

You can check out our handy marine aquarium heater wattage calculator to help you find what size of heater is right for you and your marine aquarium. You don’t have to simply purchase a heater that directly corresponds to the recommended wattage.

A Few Handy Tips – Multiple Heaters, Placement, & Thermometers

It can be very useful to buy two separate heaters that add up to the required wattage collectively. This way, if one fails, your water won’t drop too much in temperature as one heater should still be working.

You may be wondering where you should place your heaters? That’s a subject we are going to go more in depth on in an upcoming article. Needless to say, you want to place it in an area with lots of flow to make sure cold water is transferred to the heater and warm water is pushed out into the tank.

It’s a very good idea to keep a thermometer in your display and visible at all times. This is a bit of an old school way of thinking. Especially if you remember the stick on thermometers that you used to see all the time on aquariums in the 90s and 2000s. It is very helpful, though, as heaters are prone to failure.

If you have a thermometer that is easily visible, you will know straight away when something has gone wrong. I have a probe in my display all the time and a digital thermometer sitting on my lid. That way I can always be sure that my tank’s temperature is stable.

Certain thermometers can even alert you via an app or notification when the temperature drops below a certain point. This can be life saving for a delicate reef and a very worthy investment. Place your thermometer or probe somewhere in the middle of the tank and away from flow that may cause an inaccurate reading.

In Short

While marine aquarium heaters aren’t exactly a particularly interesting subject. They are a very important piece of equipment that can be vital to maintaining the health of your miniature piece of the ocean. Thanks for reading and spending your time with Simple Reefs.