Algae scrubber

An algae scrubber is a water filtering device (not to be confused with a scrubber pad used to clean glass) which uses light to grow algae; in this process, undesirable chemicals are removed from the water.^[1] Algae scrubbers have allowed saltwater and freshwater aquarium hobbyists the ability to operate their tanks the way that oceans and lakes operate: using primary production.

Concepts

Both iron fertilization and ocean nourishment are techniques that boost the primary production of algae in the ocean, which consumes massive amounts of nutrients and CO₂. It is this same consumption of nutrients that algae performs in an aquarium or pond.

An algae scrubber filters water by moving water rapidly over a rough, highly-illuminated surface, which causes algae to start growing in large amounts. As the algae grow, they consume nutrients such as inorganic nitrate, inorganic phosphate, nitrite, ammonia, and ammonium from the water.^[2] These nutrients are normally a problem in aquariums and ponds because they cause nuisance algae to grow, and also because they cause sickness and/or other problems in aquarium fish, invertebrates and corals.^[3] An algae scrubber allows algae to grow, but the algae grow inside the filter instead of in the aquarium or pond. This causes the nuisance algae in the aquarium or pond to be "scrubbed" (removed), along with the nutrients that caused the nuisance algae to grow in the first place. Nuisance algae in the aquarium or pond are not to be confused with the desired algae in the algae scrubber filter itself.

Algae scrubbers are used in both saltwater and freshwater, and remove nuisance algae of multiple types: cyano or slime, bubble, hair, Chaetomorpha, Caulerpa, and film algae, as well as dinoflagellates and Aiptasia.

History

Dr. Walter Adey

The algae scrubber was invented by Dr. Walter Adey, who in the late 1970s was Director of the Marine Systems Laboratory at the Museum of Natural History, Smithsonian Institution (Washington DC, USA).^[4] His research of various types of algae led him to try to understand how the ocean "recycles" nutrients. He built a very successful public aquarium for display at the Smithsonian: "A 130 gallon (456 liter) coral reef microcosm, that after 8 years of closure [to the environment], had its chemical parameters controlled solely by an algal turf scrubber. This system, studied by a multidisciplinary team of biologists, demonstrated calcification [coral growth] rates equal to the best 4 percent of wild reefs, and at 543 identified species, and an estimated 800 species, ranked per unit area as the most biodiverse reef ever measured."^[5]

"Recycling" means how the nutrients go from plants to animals, and back to plants again. On land, you see recycling by following the oxygen flow: Green plants use carbon dioxide, and release oxygen; animals use this oxygen, and release carbon dioxide. In oceans and lakes, nutrients go from algae to animals, and back to the algae again.

Aquatic nutrient cycle

Dr. Adey built several versions of algae scrubbers for aquariums at the Smithsonian. He called them "Algal Turf Scrubbers", because at the time it was believed that "turf" algae was the best type of algae to grow in a scrubber. He also created the first U.S. patent for an algae scrubber,^[6] which described a complex dumping device that poured water onto a horizontal surface. After several years of development, he participated in a test of a large algae scrubber on the Great Barrier Reef Aquarium: "The Reef Tank represents the first application of algal scrubber technology to large volume aquarium systems. Aquaria using conventional water purification methods (e.g. bacterial filters) generally have nutrient levels in parts per million, while algal scrubbers have maintained parts per billion concentrations, despite heavy biological loading in the Reef Tank. The success of the algal scrubbers in maintaining suitable water quality for a coral reef was demonstrated in the observed spawning of scleractinian corals and many other tank inhabitants."^[1]

He licensed his patent to very few individuals, who for a short number of years sold a limited number of scrubbers to aquarium hobbyists. The complexity of the design, however, and the cost of the license, caused the scrubber units to be very expensive. This, combined with the fact that the units were noisy, splashy, and unreliable (the dumping mechanism would get stuck) caused the sales to be slow. The scrubbers were just starting to make headway into the aquarium hobby in the 1990s when Adey decided to withdraw his license and no longer allow anybody to make or sell them. He turned his attention instead to commercial and industrial applications, and entered private business making large scale scrubber installations for lakes and rivers.^[7]

As the internet developed in the 1990s, aquarium and pond hobbyists began discussing nuisance algae problems, and started noticing a trend: Aquariums and ponds with very high amounts of nuisance algae had no detectable nutrients in the water. This at first seemed odd, since the amount of nuisance algae usually increased as the nutrients in the water increased. How could there be a very large amount of nuisance algae, but no measurable nutrients in the water to support this? Biologists then began pointing out that when the amount of nuisance algae became large enough, the algae actually consumed all the available nutrients from the water faster than new nutrients were added.

Interest in using algae for nutrient control once again increased, this time in the form of keeping the algae in a "sump" or other small aquarium which was connected to the main aquarium by plumbing. With added lighting and flow, algae would grow in this area, and the algae would consume nutrients from the water, just as Dr. Adey's algae scrubber units did. Sumps or other small aquariums used for this purpose became known as "refugiums".^[8] The name "refugium" was used because the growing algae provided a safe place for small and microscopic animals to breed and grow, and thus was a "refuge" from the large fish and invertebrates in the main aquarium that would otherwise consume them. And while the refugiums did indeed consume nutrients from the water, they did not consume them fast enough in all situations; this caused many hobbyists to continue to have nuisance algae problems in their main aquariums.

Later developments

Original vertical scrubber design

In August 2008, an aquarium hobbiest was experimenting with ways to provide filtering, and after trying to purchase an algae scrubber unit (which were no longer available), ended up just building one,^[9] since this was the only option remaining. The dumping-bucket design seemed very complex to build, thus it was reasoned that there must be an easier way of moving water across a rough surface, which essentially is all an algae scrubber does. It was decided to let gravity do the work, and thus was built a simple "waterfall" algae scrubber which used a simple PVC plumbing pipe to flow water down a piece of plastic knitting screen (also known as "plastic canvas"). The knitting screen was roughed up to allow algae to attach, and a strong light was put on both sides of the screen. The fast flowing waterfall, combined with the bright light, caused large amounts of algae to grow on the screen much like it did on Dr. Adey's units. The simple waterfall design was basically free to build, and aquarium hobbyists built them for their own aquariums (and ponds).

In almost every case, these homemade algae scrubbers reduced the nutrients to very low levels, and this reduced or eliminated all nuisance algae problems.

Undesirable brown (left), and desirable green (right) algae

In addition to finding a simpler waterfall design, it was also found that "turf" algae, which was the focus of Dr. Adey's design, was actually not as effective as "green hair algae".^[10] This is because turf algae tends to be dark brown and thick (like artificial turf on sports fields), and when it gets thick it blocks the light and water from reaching the screen. This slows the growth (and filtering) of the algae because the bottom layers of algae (that are attached to the screen) start to die and detach. Green algae, however (especially light-green hair algae), allows light and water to penetrate all the way down to the screen, allowing the algae to grow faster and absorb more nutrients without dying and losing its attachment to the screen. This is fortunate, because green hair algae is the exact type of algae that grows automatically in a properly-constructed algae scrubber.

Methods

Construction

Further information: Aquarium lighting

Pipe: A basic algae scrubber starts out with a ¾" (1.88 cm) PVC pipe, with a 1/8" (3mm) slot cut along the length of it (the slot is only on the bottom side; it does not go through to the top side). The pipe is marked with a marker, and cut with a motorized cutting tool.

Screen: A piece of "plastic canvas" (otherwise knows as "knitting screen") is purchased at sewing or crafts stores, or online. It is roughed up with a "hole saw" from a hardware store; the hole saw is dragged by hand, back and forth across the screen.

Lights: The lights are attached on both sides, and pointed to the middle of the screen. The bulbs are about 4" (10 cm) from the screen. Simple CFL (compact fluorescent) bulbs with clip-on sockets and large reflectors work well. The bulbs that say "warm" or "soft" usually work the best. The bulbs are put on a timer, so that they are on for 18 hours a day, and off for 6 hours.

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Size

The basic size of an algae scrubber is one square inch (6.25 square cm) of screen for every gallon (3.8 liters) of water in the aquarium. Thus a 100 gallon aquarium would have a screen of 10 by 10 inches, with a light on both sides.

The total wattage of the CFL bulbs is at least half the number gallons, and preferably equal to the number of gallons. Thus, a 100 gallon tank would have at least 50 total watts of CFL bulbs, which could be two bulbs of 25 watts each (real watts, not equivalent watts), and preferably 100 total watts.

The flow required is generally 35 gallons per hour, for every inch of slot in the pipe (60 lph, per cm). Thus a 10 inch slot would need 350 gph.

Cleaning

Approximately every seven days, the screen is removed from the pipe and cleaned in a sink with running water. After the algae are removed, the screen is put back in the scrubber. The pipe is removed also, and the slot is cleaned with a toothbrush, to remove any algae that have grown up into it. If the screen is not cleaned like this periodically, the algae will get too thick and block light and flow from reaching the "roots" of the algae, and these areas will die and let go, putting nutrients back into the water.^[10]

See also

• Refugium (fishkeeping)

References

1. ^ ^{a b} Nutrient Cycling In The Great Barrier Reef Aquarium. Proceedings of the 6th International Coral Reef Symposium, Australia, 1988, Vol. 2
2. ^ Algal Response To Nutrient Enrichment In Forested Oligotrophic Stream. Journal of Phycology, June 2008
3. ^ Fish Disease: Diagnosis and Treatment, Second Edition, 2010
4. ^ Smithsonian Institution, Dept. of Botany
5. ^ WalterAdey.com
6. ^ U.S. Patent 4333263, Issue Date June 8, 1982
7. ^ Hydromentia Water Treatment Technologies
8. ^ Reef Invertebrates, 2003, page 46
9. ^ Original first vertical algae scrubber design, posted on aquarium discussion forum August 2008
10. ^ ^{a b} AlgaeScrubber.Net

External links

• AlgaeScrubber.net