Re:UV sterilizer

Pete Giwojna

Dear Hilfiger:

No, sir, that’s incorrect — an ultraviolet sterilizer won’t harm larval shrimp, small crustaceans, copepods, amphipods, etc., that may enter your seahorse tank from your refugium or sump. Those are all macroscopic organisms that you can see with the naked eye; as a rule, ultraviolet sterilizers destroy microscopic organisms that are not visible to the naked eye.

In other words, UV can be very effective in reducing free-floating microalgae, bacteria, fungal spores, and microbes in general, protozoan parasites in the free-swimming stages of development, and other suspended microorganisms (Fenner, 2003a). Seahorses are prone to a number of serious bacterial problems such as Vibriosis and mycobacteriosis, and a properly installed and maintained UV sterilizer can be invaluable in reducing the incidence and spread of such infections. When properly used, UV sterilization can reduce microbial levels in the aquarium to the low levels normally found in the wild or below (Fenner, 2003a). But it doesn’t kill organisms that are significantly larger than microbes.

Nor will an ultraviolet sterilizer have any significant impact whatsoever on the good bacteria in an established aquarium, since the beneficial nitrifying bacteria and denitrifying bacteria require attachment sites in order to grow and thrive. They will proliferate within the substrate and the porous interior of live rock for example, or build up a large population within bio-balls or a sponge filter or similar filtration media, where they cannot be affected in the least by ultraviolet sterilization. An ultraviolet sterilizer can only kill free-swimming bacteria and protozoan parasites that pass directly under the UV lamp with sufficient contact time to do the job.

Having said that, neither your protein skimmer nor an ultraviolet sterilizer should be operated on a new aquarium that is still in the process of cycling. You want the "seed" bacteria to be able to freely colonize any suitable substrates at first, and you don’t want the sterilizer or skimmer removing any of the nitrogenous wastes that the nitrifying bacteria feed upon (UV radiation in the proper range of 295-400 nanometers is known to help oxidize phosphates, metabolites, organic molecules and nitrogenous compounds through the incidental production of ozone).

For best results, the UV sterilizer must be properly sized, operated, and maintained. In order to provide a good kill rate per pass, the effective dwell time (the length of time the water is exposed to UV radiation while passing through the sterilizer) should be maintained at or above roughly twenty gallons per hour flow per watt of UV (Fenner, 2003a). This sounds complicated, but selecting the right sterilizer for your needs is actually very easy. Every manufacturer provides guidelines to help the hobbyist choose a unit and a pump that provide the proper wattage, flow rate and exposure time for any given application.

To assure efficient transmission of the proper wavelengths, sleeves (i.e., the quartz jacket that shields the lamp) must be kept clean and UV bulbs must be replaced at regular intervals. Equally important, the aquarium water should be filtered before it passes through the sterilizer. For maximum efficiency, make the UV sterilizer the final component of an in-line filtration system, so that the water has already passed through your mechanical, biological and chemical filtration media before it flows through the sterilizer (Fenner, 2003a). And, as I mentioned, do not operate your UV sterilizer during the break-in period when a new aquarium is being cycled and the biological filtration is becoming established. It is counterproductive to reduce microbe levels and nutrient levels when the aquarium is cycling.

Ultraviolet sterilizers are most effective when the water is clear, they are operated continuously around the clock, and the UV bulb is replaced regularly (at least every 6-8 months).

Reef keepers tend to avoid UV because it reduces the population of microscopic planktonic organisms filter-feeding invertebrates require, but that’s mainly a consideration for reefers who will be keeping a lot of filter feeders or live corals that need supplemental feedings rather than obtaining most of their food and directly from the zooanthellae in their tissues through the process of photosynthesis. (Again, I should emphasize that the UV sterilizer may kill suspended microalgae in the form of phytoplankton, as well as bacteria and protozoans — not the larger zooplankton such as larval crustaceans, copepods or larval fish.) And if your aquarium will employ micron filtration or an ozonizer to help regulate ORP, those will provide many of the same benefits as an ultraviolet sterilizer, reducing the need for UV.

Obviously, ultraviolet sterilization is a bit superfluous in an aquarium system with an ozonizer or ozone generator, but otherwise, it can be a very worthwhile investment for the seahorse keeper.

When using an ultraviolet sterilizer on your aquarium, always observe the following precautions:

Never operate UV until the aquarium has cycled completely and the biological filtration is fully established.

Never operate UV when the aquarium is being treated with drugs or medications of any sort.

Always unplug the sterilizer before working on it to clean the quartz sleeve or replace the UV bulb in order to prevent possible shocks in case the unit should break or become wet.

Unshielded UV light can be damaging to the human eye so NEVER look at the UV bulb with your naked eye while it is operating.

All things considered, I’m generally pro-UV for most conventional seahorse setups. I would say UV sterilization is a must for anyone who’s keeping delicate wild-caught seahorses or seahorses obtained from your LFS. If you’re keeping captive-bred-and-raised seahorses obtained directly from the breeder — particularly a High-Health aquaculture facility such as Ocean Rider — then an ultraviolet sterilizer becomes an option rather than a prerequisite. If you can afford it and your aquarium system allows for easy installation and maintenance, it’s still a nice addition to a seahorse tank that can help minimize any potential problems with certain microbes and free-swimming protozoan parasites and which does a great job of helping to control nuisance algae. It can be especially helpful for controlling the incidence and spread of disease in crowded nursery tanks and grow-out tanks.

Those are just some of the things to keep in mind when deciding whether or not an ultraviolet sterilizer is a good option for your particular needs and aquarium system.

Best of luck with your seahorse system and refugia, Hilfiger!

Pete Giwojna

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