The Un-Filters 401 Chapter 1
Ultra Violet "Sterilizers" vs. "Clarifiers"
After the convoluted argument above it should come as no surprise that the typical pond Ultra Violet “Sterilizer”, which really isn’t a filter, doesn’t really “sterilize” either, at least not in the sense of “to kill all microorganisms and render the environment sterile”. At the energy levels that they are typically used in ponds, what they do is render some algae incapable of reproducing. Now, that doesn’t mean that UV can’t be used to KILL lots of different organisms, from algae to bacteria, even some viruses, at extremely high exposure levels, and some facilities do exactly that, like hospitals, research labs, pisciculture facilities and the like, where “rendering the environment sterile” is critical. For example (and only to illustrate the difference between this use and typical pond dosages), Aquatic Ecosystems of Apopka Florida, a leader in pisciculture and aquatic equipment, used to zap the water in their Zebra Danio tanks, where they raised fish used for scientific research, with 88 THOUSAND microWatts per second per square centimeter (88,000 µW/s/cm²). In comparison, it takes only about 15 microWatts per second per square centimeter (15 µW/s/cm²) to render most free-floating algae cells, the kind that make green water, “sterile” in the sense of “incapable of reproducing”. No wonder it’s confusing! What’s important is the idea that, even at relatively low exposures, exposure to UV light can be effective at reducing free-floating algae, not by killing, but by preventing the cells from reproducing, multiplying and turning the water green. Since algae cells don’t live all that long, if they can’t reproduce, you win the war by attrition, as cells die off faster than they are replaced, eventually clearing or “clarifying” the water. The better term for them, then, describing what they achieve, is “Ultra Violet Clarifier”. Let’s take a look at actually how UV clears green water, when to use it and why it’s not a cure-all.
After the convoluted argument above it should come as no surprise that the typical pond Ultra Violet “Sterilizer”, which really isn’t a filter, doesn’t really “sterilize” either, at least not in the sense of “to kill all microorganisms and render the environment sterile”. At the energy levels that they are typically used in ponds, what they do is render some algae incapable of reproducing. Now, that doesn’t mean that UV can’t be used to KILL lots of different organisms, from algae to bacteria, even some viruses, at extremely high exposure levels, and some facilities do exactly that, like hospitals, research labs, pisciculture facilities and the like, where “rendering the environment sterile” is critical. For example (and only to illustrate the difference between this use and typical pond dosages), Aquatic Ecosystems of Apopka Florida, a leader in pisciculture and aquatic equipment, used to zap the water in their Zebra Danio tanks, where they raised fish used for scientific research, with 88 THOUSAND microWatts per second per square centimeter (88,000 µW/s/cm²). In comparison, it takes only about 15 microWatts per second per square centimeter (15 µW/s/cm²) to render most free-floating algae cells, the kind that make green water, “sterile” in the sense of “incapable of reproducing”. No wonder it’s confusing! What’s important is the idea that, even at relatively low exposures, exposure to UV light can be effective at reducing free-floating algae, not by killing, but by preventing the cells from reproducing, multiplying and turning the water green. Since algae cells don’t live all that long, if they can’t reproduce, you win the war by attrition, as cells die off faster than they are replaced, eventually clearing or “clarifying” the water. The better term for them, then, describing what they achieve, is “Ultra Violet Clarifier”. Let’s take a look at actually how UV clears green water, when to use it and why it’s not a cure-all.
