Marla Sanchez, Alan Meier

Lawrence Berkeley Laboratory
June, 1997
previously published as "The Rage for Aquaria"
in Home Energy Magazine Sept/Oct. 1997

Residential energy auditors often dismiss or overlook aquaria in their assessments. Yet nearly one in every 12 households owns at least one aquarium. Depending on the equipment used, the tanks can draw a surprisinglly large load and occasionally qualify as the single largest end use in a home.

Most freshwater aquarium setups include fouorescent lighting, a filter and an aerator. Three basic types of aquarium filters are:

• Canister filter-large plastic canisters that have a powerfull pump that forces water through a dense filter medium at high pressure.
• Power filters-plastic cartridges that fit inside the aquarium. Water is drawn into the filter by a pump and allowed to trickle back into the tank.
• Under-gravel filters (UGFs)-aerator creates a current that draws water through a gravel filter.

Aerators are commonly used in smaller tanks with UGFs or when there are few plants or lots of fish, requiring more dissolved oxygen in the water. Aerators are also used with bubble wands-decorative devices that create a stream of bubbles in the tank. Aerators are not necessary with larger tanks that have a power or canister filter, since these devices provide sufficient water movement during filtration to oxygenate the tank.

Basic prototype tank set ups were assembled based on information provided by aquarium store employees and communication with many fish hobbyists. From this data, we constructed three different prototype aquaria and calculated the energy consumption of each (Table 1). In most homes with fish, the aquarium rarely uses more energy than the microwave oven.

*Values are based on use of one or two 10W-20W fluorescent light tubes with 10 hour per day run times; 4W-15W filter with 24 hour run times; and 1.5-4W aerators with 24 hour per day run times.

Though the above energy consumption values are reliable estimates for average tanks, several situations can be encountered in which energy use will be higher. If a tank is heavily planted, lighting requirements are much higher. If the tank is a salt water aquarium, pumps (Powerheads) that increase water movement add a substantial amount of energy.

The lighting requirement of a densely planted tank is approximately 2 watts/gallon. A small tank requires 20 W of lighting and the annual energy consumption ranges from 110-140 kWh. Medium tanks require nearly 60 W of lighting and consume 300-340 kWh/yr. The lighting requirement of a large tank is over 100 W and energy use ranges from 570-630 kWh/yr.

Salt water tanks have similar lighting, heating and filtering needs described in the basic tank prototype. Energy use is increased in salt water tanks due to Powerheads. The number of powerheads in a tank varies by home. Small tanks typically have two mini-powerheads. Each powerhead is rated at 8 W and runs all the time. Power heads in small tanks use 140 kWh/yr and tank energy consumption ranges from 230-260 kWh/yr. Medium and large salt water tanks have two large power heads rated at 25 W/ea. Power heads in these tanks use 440 kWh/yr. The electricity consumption of a medium salt water tank ranges from 600-630 kWh/yr and large tanks consume 710-770 kWh/yr.

Reef tanks are the largest and most complex of all aquaria. Generally, reef tanks also consume the most energy. Energy use is tremendous because of the lighting requirements, temperature requirements and the powerful pumps used to circulate water.

The typical reef aquarium is set up as a tank and sump combination system. Water comes from the main tank to a smaller tank in a stand below (the sump). Attached to the sump is a powerful pump which returns the water back to the main tank. A separate pump drives a protein skimmer which removes amino acids, lipids, phosphates and other nutrients to prevent algae growth. Powerheads are also used in reef tanks. The powerheads are typically controlled by a Wavemaker. Because corals do best when the water surges in different directions, the wavemaker turns powerheads on and off to make random water movements across the corals.

The lighting requirement of a reef tank is 6 W/gallon. The heat generated by the enormous amount of lighting and the powerful pumps frequently creates tank temperatures well above the target (75°). As a result, reef hobbyists need to cool (rather than heat) their tanks. Fans are located beneath the tank lights. The fans blow across the water surface, increasing evaporation and cooling the tank. Some tank set ups include an actual mini-AC unit attached to the tank. Due to the enormous first cost and operating costs of the AC unit, most hobbyists prefer cooling fans. In the summer, the cooling fans run all the time. During non-summer months, cooling fans run only when the lights are on.

How much energy do reef tanks use? This is a difficult question. Most reef tanks are relatively large, so we only created two prototype tanks (55 gallons and 180 gallons). Fifty five gallon tanks use approximately 3000 kWh/yr. One hundred eighty gallon tanks use over 6000 kWh/yr. To put these numbers in perspective, the energy use of a smaller reef tank is greater than the combined annual energy consumption of a residential central air-conditioning system and home lighting. Energy from a large reef tank exceeds the combined annual electricity consumption of a residential central electric heating system and a refrigerator.

In the U.S., approximately 8% of households own an aquarium. Ninety percent of aquariums are freshwater tanks; 9% are salt-water (non-reef); and 1% are reef tanks. Using survey data from the Pet Product Manufacturer Trade Association, national energy use of aquaria is estimated at 2.4 TWh/yr. Freshwater tanks account for about half of all aquarium energy use. Amazingly, reef tanks (reefs represent only 1% of all aquarium owners) are responsible for over one quarter of all aquarium energy consumption. Salt water tanks account for the remainder. It is certainly worth noting that 10% of tanks (marine tanks) account for half of all aquarium energy use.

We would like to thank the many aquarium hobbyists (subscribers to rec.aquaria.misc) who answered our barrage of questions regarding their tank set ups. Without their zealous and informative responses, we would not have been able to estimate reef tank energy consumption. Also thanks to Brian Pon (LBNL) whose help allowed us to circumvent the many practical problems associated with researching aquaria.

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