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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Algae scrubber | 2/3 | https://en.wikipedia.org/wiki/Algae_scrubber | reference | science, encyclopedia | 2026-05-05T09:00:37.646457+00:00 | kb-cron |
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 was granted the first U.S. patent for a dumping-bucket algae scrubber, which described a complex dumping device that poured water onto a horizontal surface, thus simulating waves in a reef environment. 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 [much lower], 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." Unfortunately, it was not known at the time (1988) that calcium and alkalinity needed to be added to an enclosed reef tank, in order to replace that which is utilized by the growing calcifying organisms. Even five years after that, the Pittsburgh Zoo was just starting to test a "mesocosm" scrubber reef tank to see if calcium levels would drop: "It was hypothesized that Ca2+ and the substitutive elements Sr2+ and Mg2+ might have reduced concentrations in a coral reef microcosm due to continuous reuse of the same seawater as a consequence of the recycling process inherent in the coral reef mesocosm." [...] "The scleractinians (Montastrea, Madracis, Porites, Diploria, and Acropora) and calcareous alga (Halimeda and others) present in the coral reef mesocosm are the most likely organisms responsible for the significant reduction in concentration of the Ca2+ and Sr2+ cations." [...] "Ca is not normally a biolimiting element, and strontium is never a biolimiting element; HCO3 [alkalinity] can be. It appears that, because of a minor limitation in the design parameters of the mesocosm, these elements and compounds may have become limiting factors. [...] It is surprising that the organisms could deplete the thousands of gallons of seawater (three to six thousand) of these elements even within two or more years." After other researchers added calcium and/or connected their tanks to the ocean (which also supplies calcium and alkalinity), corals began growing again. Nevertheless, "problem" nutrients (ammonia, ammonium, nitrate, nitrite, phosphate, CO2, metals) were always kept at very low numbers. Dr. Adey licensed his patent to very few individuals, who for a short number of years sold a limited number of aquarium scrubbers to 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. 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 should increase 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, as Dr. Adey had theorized. 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 via 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". 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. However 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.
== Modern forms ==
More recent variations are built with a simple "waterfall" driven by gravity, using a PVC plumbing pipe to flow water down a piece of plastic knitting screen (also known as "plastic canvas"), which is roughed up to allow algae to attach. In almost every case, these homemade algae scrubbers reduced the nutrients to very low levels, and this reduced or eliminated all nuisance algae problems.