Heating your marine tank

Taking the mayhem out of marine fish keeping




Ideally you want to maintain a constant temperature of around 77-79 degrees Fahrenheit or 25 degrees Celsius. Your marine tank inhabitants will appreciate the temperature staying as stable as possible. If you read the water parameters page you will see the importance on keeping everything in the tank as stable as possible. If you consider that rising or falling temperature also changes salinity then you’ll see that there is more to keeping the temperature stable than just maintain heat for heats sake.


There are plenty of heaters on the market that are more than adequate to heat your marine tank (make sure you do use a salt water friendly heater) but it’s often worth two rather than one heater. If one heater fails then at least you’re not faced with wrapping the tank in blankets whilst trying to find a replacement. Two heaters also ensure that a single heater isn’t overworked and heats the tank much more evenly.




The length of your heater should be suited to the height of your tank. As heat rises a short heater in a tall tank will not heat the water efficiently. You should try and use a heater that fits the height of the tank where possible. Always remember to unplug your heater if doing water changes and it will be out of water for any length of time. They will over heat and shatter very easily if trying to heat when dry.


Remember that other aquarium equipment will also heat your water. You need to consider this when sizing up the appropriate sized heaters. The ambient temperature of the room the marine tank will be located in will also influence your choice. The general rule of thumb is 1 watt per litre of water under normal conditions where there is a difference of around 5-10 degrees between your ambient temperature and your desired tank water temperature.


All heaters will come with a rating on the packaging anyway, it is worth mentioning that many people (myself included) take their heaters for granted, leave them untouched for months (or years…) then wonder why they have suffered from a tank crash. The thermostats on the heaters can get ‘stuck’ if they’re never touched. Every once in a while it can be worth fiddling about with the thermostat knob turning it up and down a few times then resetting it just to ‘wake it up’ a bit.



Helpful tips




It's always better to use two heaters instead of a single one. This will give back up incase one fails and create a more even distribution of heat throughout the tank.


Try to reduce any temperature fluctuations as much as possible, your marine tank inhabitants crave stability and fluctuation temperatures can throw out your tank chemistry quite significantly.

Heaters - in a nutshell

As a general rule you can usually work to 1 watt per litre if the tank is located in a 'normal' room in your house

Make sure your heater is suited to the size of your tank, a short heater in a two foot tall tank will not work efficiently.

Remember to check your heater regularly, it's easy to forget abouth them but remember the thermostats can fail.

Remember to check the wiring on your heater regularly, especially if you keep an urchin, they can (and will) graze through the protective outer casing over a period of time.