Electrical power is an integral part of a marine aquarium. We rely on it for lighting, heating, cooling, filtration and circulation. Unfortunately, mains power is not 100% reliable. Storms, bushfires, road accidents and a variety of other causes can result in power outages of varying lengths. As aquarists we must acknowledge the potential for power outages and plan for their eventuality.
While we run a myriad of devices off mains power the only really important thing to provide in the event of a power outage is gas exchange and circulation. Oxygen is necessary for all the organisms in the tank (with the exception of anaerobic bacteria deep in the sand bed or live rocks) and it is imperative that the organisms will receive sufficient oxygen at all times, including when mains power is out. To achieve sufficient oxygenation (and removal of carbon dioxide) some form of water movement is necessary, including increasing the surface area of the air/water interface. Turning over the tank volume 2 times per hour should suffice but 5 times per hour would be ideal.
There are two basic ways to provide circulation and gas exchange in the event of a power outage (discussed below):
Lighting is generally unimportant during a power outage. Most photosynthetic organisms will have no problems at all going for a few days with little or no light. As lighting generally requires a lot of power it is usually best not to attempt to light the tank during a power outage. This may mean slightly less oxygen and more carbon dioxide in the water as there will be no photosynthesis but this situation can be handled via circulation.
Unless the environment is particularly cold, heating should not be a problem during power outages. Like lighting, heating requires a fair amount of power, attempting to heat the tank during a power outage is going to draw significantly on the alternate power source(s). In a cold environment with extended power outages, it may be necessary to heat the room using non-electrical heaters such as gas or wood. Heating water on a gas stove and floating sealed containers in the tank of sump with the heated water may be of benefit. Allowing the tank temperature to drop a few degrees should not present any major problems to the inhabitants and should reduce the demand on oxygen by lowering the metabolic rate of the organisms.
Cooling may become an issue in hot environments. Coolers generally use too much power to be of use during a power outage. Small fans blowing across the tank may provide enough cooling through evaporation. If necessary battery operated fans can be used or fans with low power loads plugged into an alternate power source.
If a power outage occurs under very hot conditions, other actions may be necessary to specifically cool the tank. While the oxygen concentration in the aquarium water may decrease slightly due to an increase in water temperature, the affect of a temperature increase on the metabolic rate of the organisms in the aquarium could be significant. An increase in water temperature of 10°C could result in more than doubling the metabolic rate of any organisms and this would translate into more than doubling of the oxygen consumption. This will compound the effect of any lack of circulation due to the power outage. Additional means of cooling a tank could include:
Non-mains powered devices are usually more efficient as the devices are designed to work at lower voltages and are usually direct current based. This means that power is not wasted in converting from direct current to alternating current and from raising the voltage to mains voltage. However, in most cases, you would need to be home in order to place the alternate circulation device into the tank.
Battery operated air pumps are inexpensive and can provide sufficient gas exchange and circulation in lightly stocked tanks. Multiple may be required for larger tanks. It may be possible to leave the airstone(s) in place in the tank and connect the pump to a switch which turns on the pump in the event of a power outage.
12V DC bilge pumps can be operated directly from a car battery (including one still in the car) and will move a lot of water. For example, the Rule 1100 GPH 12V Bilge Pump will move almost 4000 litres per hour with no head when running off 12V DC and draws around 40 watts. This pump should run for 6 hours from a 20AH battery. Smaller pumps are available that will draw as little as 24W (run for 10 hours on a 20AH battery). Consideration should be given to the size of the pump and the power it requires. The larger the pump, the more circulation it will provide, but the more power it requires and so will not be able to be run for as long.
Using an alternate source of mains level power allows the use of the existing circulation devices in the tank and merely provides the power to run those devices. You should not place all the normally used circulation devices on the alternate power source as this will decrease the operating life during the power outage. Choose enough pumps or powerheads to provide 2-5 times tank volume turnover per hour.
Uninterruptable Power Supplies (UPS) intended for computer systems provide effective off-the-shelf solutions to providing power to circulation devices in the event of a power failure. The only work required is to unpack the UPS, plug in the required circulation devices and plug the UPS into the mains. With power to the mains the devices will work as normal and the battery in the UPS will be charged. In the event of a power failure, the UPS will automatically cut over to its battery providing an uninterrupted supply of power to the devices plugged into it. There is a large range of brands and models of UPS available, each with different features and battery operating time. Most manufacturers provide online tools to determine the model required for the required load and battery operating time.
While a UPS is very easy to use, you are paying for an unnecessary feature: instantaneous cutover of power. For in tank circulation, it is not necessary to cut over immediately. In fact, it would make little difference if the cutover took a matter of minutes. Additionally, UPS only have a life of around 3 years, and while the internal battery can be replaced, if anything goes wrong with the circuitry, the whole UPS must be replaced.
Inverters are devices that convert 12 or 24 volts DC to AC at mains voltage. They are available in a number of makes and models to provide different maximum loads of power. There are relatively inexpensive, can be plugged directly into cigarette lighter socket of a car and provide a standard mains type socket. Most are also provided with clips to allow them be connected directly to battery terminals. Ensure you purchase an inverter to provide all the required load. As with any electrical device, the more power it uses, the faster it will drain a battery (that is not being charged). They are not 100% efficient and so some power is lost in the conversion. If a 50W load is being drawn from the inverter, the invert itself may draw over 5A at 12VC. With this sort of load, a 20AH battery would last around 4 hours.
An inverter can be run off any battery source and a car battery could be used while not mounted in a car. Am inexpensive mains power charged can be used to keep the battery charged when not in use.
One of the drawbacks with a straight inverter is that you need to be home to move the circulation devices from the mains supply to the inverter and plug the inverter into a suitable 12VDC source - such as the car. It is possible to build a battery backup power supply which gives similar capabilities to a UPS with better battery operating life at a fraction of the cost. See: Backup Power for instructions on creating such a device.
Fuel driven generators can provide a significant amount of power for extended periods of time - only limited by the supply of fuel. They can be purchased or rented and available in models that run off diesel or unleaded fuel. Even small generators could provide sufficient power to run more than just basic circulation, including heating/cooling and lighting. Preference should be given to circulation. A generator could also provide power for other household devices. It should be noted that generators are quite noisy and should be operated in a well ventilated area.
Solar or wind collecting devices provide an alternate power source or a method of charging batteries for alternate power sources.
Last updated: 18 July 2004