Not All Ultraviolet Sterilizers Are the Same
Green water freshwater aquarium, before and after UV sterilizer
Nor should all ultraviolet (UV) sterilizers be used with the same intentions.
I’ve always been a proponent for UV on aquaria and ponds for the reduction of diseases. When set up properly, UVs will lower numbers of waterborne bacteria, viruses, protozoa and algae. They work by altering the single-celled organisms’ DNA chemical bonds. In essence, this will eliminate a microorganism’s ability to reproduce, assimilate or cause harm.
This is the most important part of a marine system with regard to parasitic disease and bacteria control. Oversizing is recommended when choosing a suitable sterilizer. Keep in mind, the effective qualities of a UV are determined by the power of the bulb (quality/brand), distance of water from the bulb (housing) and flow rate past the bulb (dwell time). These are where problems exist within subpar manufactured UVs. They may be design flaws or overstatement of their true proficiency.
Not considering dwell time and only using wattage ratings, many UV manufacturers tend to overstate the uses and abilities of their product (C Strohmeyer; americanaquariumproducts.com/AquariumUVsterilization.html).
In Strohmeyer’s in-depth article on UV use, he explains how a 9-watt bulb in 5 inches of housing is not necessarily better than an 8-watt bulb in 11 inches of housing. Remember, the power of the bulb times the exposure of UVC radiation within a housing determines the strength of irradiation. Thus, the physical construction of a unit tested by microbiologists is important to consider for proper validation of the manufacturer’s claims. This is the argument behind submersible UVs and overflow or canister filters with built-in UVs. They cannot produce the proper mw/cm2 needed for protozoa or bacterial irradiation. They simply are not sufficient for pathogen control and more appropriate for water clarification. Another way to look at it is like a heater in an aquarium. A submersible heater is like a tube-flow UV compared to a heat lamp over the surface, which is analogous to a canister UV. Think about which is more efficient to maintain thermal regulation of the entire tank.
The quality of the bulb is probably the most important component. Bonafide sterilizers use hot cathode/low pressure lamps. These bulbs emit proper UVC emission as opposed to cold cathode/medium pressure bulbs. The latter are generally used in nail salons because they are inexpensive and do not emit dangerous levels of UVC. Rather, they peak in the UVB range (S. Wright; uvsterilizerreview.com/). This is where consumers are “tricked.” They are misled by low prices and exaggerated ads to believe they are getting a sufficient product. In reality, they are purchasing a low-grade bulb not made for the irradiation of microfauna. Another problem is the purchase of units with cheap ballasts where the ballast doesn’t have the ability to fully power the bulb into the UVC range. These can be referred to as level 2/3 sterilizers whereas they are best used as water clarifiers only.
I recommend researching to learn which manufacturers design proper microbial irradiation units. We carry both high-end and level 2/3, overflow/canister types. We also understand the abilities of both and make the proper recommendation regarding usage to our clients. Cheaper choices aren’t always bad, so long as your client understands its limitations.