Potentially harmful microorganisms exist in all saltwater systems. A UV sterilizer can help eliminate harmful bacteria, algae spores, and protozoa in a marine system.

Bacteria, algae spores, and protozoa exist in every saltwater aquarium. That’s just a fact. Microorganisms can contribute to algae blooms in the tank and common parasitic illnesses from which marine fish suffer. While there are many methods to combat potentially harmful microorganisms, UV sterilization is one of the best, and should be included as a basic filtration device on all saltwater aquarium systems.

UV stands for “ultraviolet,” and UV light with wavelengths ranging from 200 to 280 nanometers is highly effective when it comes to killing waterborne pathogens. This is what is known as the UV-C spectrum or the germicidal spectrum. UV light with a wavelength of 264 nanometers is the most effective germicidal light. UV light is just beneath the visible light spectrum.

In the aquarium, water flows through the UV sterilizer where it is exposed to UV-C light that is very close to a wavelength of 264 nanometers. This process causes the water to be irradiated, killing or sterilizing waterborne pathogens and other potentially harmful microorganisms.

UV Sterilizers come in both in-line models and hang-on-back (HOB) models. An in-line UV sterilizer in an open system utilizing a sump should be mounted after the sump and, more importantly, after all other filtration devices. HOB UV sterilizers are best used on smaller systems. An HOB UV sterilizer generally pulls water from the tank by way of a powerhead.

In order for any UV sterilizer to be effective, you must consider the wattage of the bulb and the flow rate of the water through the sterilizer.

 

The effectiveness of any UV sterilizer is determined by the UV bulb wattage, the age of the UV bulb, how clean the quartz sleeve is and the flow rate of the unit. Wattage on commonly available units ranges from four watts to 240 watts. The higher the wattage, the greater the efficiency of the sterilizer and the higher the flow can be (the water needs less time in the sterilizer to be irradiated). Generally the aquarist matches the bulb’s wattage to the tank volume. For example, an eight-watt bulb might be appropriate for a nano tank (or any tank up to 50 gallons), while a 40-watt bulb would be more appropriate for a 150-gallon tank).

In conjunction with wattage, flow rate affects what microorganisms are killed in the UV sterilizer. Parasites are harder to kill than say algae spores, and so if you are targeting parasites, you will need to slow down the water flow to be effective. The reason for this is because of the so-called “dwell time” required. Dwell time is nothing more than the length of time water stays (or dwells) in the sterilizer on each pass. Because different organisms can survive different amounts of radiation, flow rate must be adjusted to the appropriate dwell time depending on what you are trying to kill. Water flow is often controlled with a ball valve and bypass system. Each manufacturer will provide appropriate flow rate and wattage combinations.

In addition to bulb wattage and flow rate, a UV sterilizer’s effectiveness is influenced by how well maintained the sterilizer is. Be sure to follow the maintenance instructions carefully. Also, don’t use a UV sterilizer during the cycling of a new tank. You must also turn off the sterilizer when using certain medications (e.g. copper-based medications).

Plan to spend anywhere from $60 for a HOB four-watt UV sterilizer to well over $1000 for a 240-watt UV sterilizer.

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