Should I Use a UV Sterilizer? by Kenneth WingerterThe two most hated things for a saltwater aquarium keeper are fish diseases and “bad” algae. Some hobbyists make an attempt to go all out against these threats by using an ultraviolet sterilizer. At least in some cases, a properly sized and properly installed sterilizer unit can indeed help to reduce the incidence of disease or algal blooms. However, they are never foolproof. And, even more notably, their use does not come without a price. Here we examine the limited benefits UV sterilization as well as some of the drawbacks. We shall begin by describing how UV sterilizers work. Ultraviolet Sterilizers – Shot in the dark Germicidal ultraviolet radiation kills microorganisms in two different ways. In the first, it disrupts the organism’s genetic material (DNA), thereby outfight killing it or rendering it incapable of reproducing. In the second, when applied to aqueous environments (e.g. aquariums), it generates toxic oxidants that degrade the organism’s vital organelles (cell membrane, chromosomes, etc.). When it comes to a particular UV sterilizer unit’s killing efficiency, exposure is everything. Much more intense and prolonged exposure is required to kill larger organisms. Thus, UV is by far most lethal towards microorganisms (i.e. bacteria and archaea) and extremely tiny algae such as Nannochloropsis. Lethality for a comparatively large and well protected diatom such as Thalassiosira is considerably lower. Only the most intense UV light and longest exposure times are capable of killing the “huge” cells of parasitic protozoans such as Cryptocaryon. One additional factor in the overall effectiveness of a UV sterilizer is the spectral output of its bulb. Some wavelengths within the ultraviolet range are more lethal than others. The UV range is divided into UV-A, UV-B and UV-C. UV-A (320-400 nm) is least effective; however, when emitted from some aquarium lights, it can cause burning of corals by harming zooxanthellae. UV-B (280-320 nm) is perhaps a bit more destructive to living tissues, but still isn’t all that lethal to most organisms. UV-C (200-280 nm) is certainly the most deadly to small lifeforms and is the wavelength most frequently encountered in UV sterilizers. Specifically, most sterilizer bulbs emit wavelengths of around 254 nm. Where you plumb your unit matters. Some aquarists like to conceal the unit within the cabinetry, running it so that it draws water from, and empties back into, the sump. However, this reduces the unit’s efficiency (especially in systems with smaller sumps or low system turnover rates) because it essentially keeps redrawing the same water over and over again. Only slightly better is plumbing the unit inline to your main filter system, just before water is returned to the display tank. The ideal is to draw water into the sterilizer from the sump and return it directly into the display. This not only prevents re-recirculating the same water, but it also makes cleaning, bulb changing and fine-tuning the flow rate a lot easier. The killing efficiency of a given UV sterilizer unit at a given time depends upon several factors. These include: Power (intensity) of the bulb(s). The age of the bulb(s). Bulb/water temperature. Aquarium water turbidity. Amount of detritus, biofilm or mineral deposit on the protective inner sleeve. Distance between the bulb and the target organisms. Type and size of the target organisms. Duration of target organisms’ exposure. Plumbing configuration. Quite often, for UV sterilization to be very effective (especially against fish parasites), the aquarist must obtain a substantially “oversized” unit. If you really want your next unit to kill stuff, be sure to read the ratings on each box very carefully as you shop. Remember that ratings for saltwater applications are significantly lower than those for freshwater applications. Many manufacturers provide two sets of ratings: One for “clarification” and another for “sterilization.” Clarification means that at a given flow rate, the unit is capable of killing water-coloring microbes and microalgae only; true sterilization implies that even with all things considered (average water turbidity, average distance of target organism from the bulb, etc.), the unit can kill most common protozoa. Limitations and disadvantages There are some disadvantages to using Ultraviolet sterilization over other types of sterilization. For example, whereas ozone sterilization is effective throughout a larger treatment zone (reactor, skimmer, sump, etc.), UV sterilization can only kill those organisms that pass right through the unit. Thus, nuisance benthic (filamentous or film) algae can spread without interruption. Similarly, some parasites can drop their eggs onto the aquarium substrate where they may develop without harm. Frankly, there are also some clear disadvantages to using any kind of sterilization. The biggest downside is loss of beneficial plankton. Think about it… Killing our phytoplankton and bacterioplankton have two undesirable results. The first reason is that without these primary producers, your nitrate and phosphate levels can go out of whack (usually toward excess). Yes, whether you carbon dose or not, these organisms sequester significant quantities of nutrients! The other reason is that these tiny plankton are a natural and hugely important source of nutrition for many filter-feeders including corals. And most reef aquaria already suffer from a lack of plankton to begin with! None of this is to say that UV sterilizers are inherently bad. For example, they very effectively help to prevent the spread of disease when used in quarantine systems. You should, however, be aware that sterilization unavoidably presents some sacrifices. Thus, in our opinion, if you have issues with bad algae or with disease, improving your husbandry/maintenance practices should always be the first resort!
mlashawnbenton says October 26, 2020 at 1:47 pm I stand by UV steralizers, I have them in all my tanks Reply
jose.caraveo1 says October 26, 2020 at 1:58 pm I will consider using one before I use chemicals again! Thank you for the info. Reply
chrisj7705-8921 says October 26, 2020 at 1:51 pm Uv sterilizes are great at controlling all types of pests Reply
Brandon Rush says October 26, 2020 at 2:08 pm UV’s are the way to go. Best solution for the clearest water Reply
jeffery486 says October 26, 2020 at 2:16 pm I’ve been interested in trying out a UV Sterilizer this article helps clarify Reply
Timothy Pugliese says October 26, 2020 at 2:21 pm I enjoyed this article! Love my UV sterilizer, would not run another tank without one. Reply
Andrew Shorez says October 26, 2020 at 2:36 pm UV sterilizers are essential when first starting any reef aquarium to prevent certain algae and ich from populating in your tank Reply
Jesse says October 26, 2020 at 2:50 pm UV sterilizes work great, long as they are sized correctly for the size of tank you are using it with. Reply
blue2bulldog says October 26, 2020 at 2:59 pm Honestly, I find quarantining everything in a separate system and keeping nutrients in check more useful than UV systems. Also having clean rodi water to match your parameters helps cut down unnecessary issues like algae. The water doesn’t need to be extra sterile, parameters just need to stay in check and quarantine procedures/treatments for all organisms need to be put in place and maintained. 🙂 Reply
deborahharper2020 says December 20, 2020 at 9:37 am I have a question for you on the quarantine procedures. I have set up a quarantine tank (been cycling since October 27) and a display tank (been cycling since November 27). I am still waiting on my first batch of fish (coming from usquarantine fish) which will go into a methylblue dip and then into my observational qt for 30 days. My question is on CUC and inverts. Do they also go through a quarantine process – and what sort? I know meds don’t work, and I am not sure on dips, or do they just get observation time? If ich or something else were riding along, would 30 days in the qt work (as long as it is fishless)? This has been a burning question as I am getting closer to having fish. Any thoughts on this would be appreciated. Reply
B says October 26, 2020 at 3:19 pm With UV being so new, it will be interesting the long term effects of running one. Reply
tsartors94 says October 26, 2020 at 4:03 pm Love my uv sterilizer. Makes the tank really clear. Reply
Patrick Jennings says October 26, 2020 at 4:03 pm I currently utilize a 40 Watt Pennair UV Sterilizer for my Red Sea XLL 625, I believe it does the job it’s intended to do. Reply
trevorpem10 says October 26, 2020 at 4:22 pm I use UV and I love it… just let the tank cycle first before turning it on. Reply
devon maynard says October 26, 2020 at 5:30 pm Great article but i will hold off on uv till ive got other things figured out don’t need to add to the learning just yet. Reply
Victoria Joy Brewer says October 26, 2020 at 7:34 pm I’ve never had any reason to run one but I may try it out in the future Reply
Dallas T. says October 26, 2020 at 10:29 pm I like the idea of using a up sterilizer — wish list! Reply
devaji108 says October 27, 2020 at 9:51 am I have a pentair 40W going my my RS650P 1st trying one really looking forward to it. Reply
zadok jollie says October 28, 2020 at 7:27 am I have always wanted one but now I want one even more. Reply
rpkneumann says October 28, 2020 at 8:32 am Thank you for the information. I use chemicals instead. Reply
Tanner Funai says October 28, 2020 at 4:56 pm UV Sterilizers can be useful. I always keep new ones on hand or hooked up to tanks in case necessary. Reply
Tanner Funai says October 28, 2020 at 4:57 pm UV Sterilizers are a great tool to utilize all the time or as needed. Reply
Scott says October 29, 2020 at 8:45 am UV sterilizers should definitely be used from the start to help control pests and algae. Reply
Leo says October 30, 2020 at 6:30 am I always use a UV sterilizer. If I assume it does nothing else (which it does, I just don’t like debating it…haha) it keeps my water crystal clear and I don’t have to crank up my lights as much. Reply
Leo says October 30, 2020 at 6:30 am I always use a UV sterilizer. If I assume it does nothing else (which it does, I just don’t like debating it…haha) it keeps my water crystal clear and I don’t have to crank up my lights as much. Reply
ed.leslie says October 30, 2020 at 7:11 am Installed UV system because many long time reefers recommended it. Reply
Mark says October 30, 2020 at 8:35 am I have one running in my 125 Dt and sump. It a better way to help run your reef Reply
Eric Brown says October 30, 2020 at 9:08 am They seem great except for losing you photo and other pods. Reply
jason.kkemp101 says October 31, 2020 at 6:33 am I love my UV, have my apex run it 4 hours in the a.m. and 4 hours in the p.m. Reply
Larry Moore says October 31, 2020 at 9:22 am The fact that the sterilizer only works on those “creatures” that pass directly under the light would seem to indicate that UV is less effective than I first believed. However, instead of resorting to the wholesale use of chemical agents, I would certainly use UV first and then for once a limited time. Reply
Brad Biliter says December 28, 2021 at 11:35 am I love my phyto and pods. I plan to add Uv in direct flow line. As pods grow larger are they cycled through the plumbing each time the tank turns over? I assumed not but I’m asking bc I don’t know. Also is phyto always in the plumbing flow? I ad phyto couple times per week. How much decimation will phyto and pod numbers experience? Generally? Thanks. Reply
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