The 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
I stand by UV steralizers, I have them in all my tanks
jose.caraveo1 says
I will consider using one before I use chemicals again! Thank you for the info.
Shawn Innes says
Agreed
chrisj7705-8921 says
Uv sterilizes are great at controlling all types of pests
Brandon Rush says
UV’s are the way to go. Best solution for the clearest water
jeffery486 says
I’ve been interested in trying out a UV Sterilizer this article helps clarify
Timothy Pugliese says
I enjoyed this article! Love my UV sterilizer, would not run another tank without one.
Andrew Shorez says
UV sterilizers are essential when first starting any reef aquarium to prevent certain algae and ich from populating in your tank
Jesse says
UV sterilizes work great, long as they are sized correctly for the size of tank you are using it with.
blue2bulldog says
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. 🙂
deborahharper2020 says
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.
meganpratt27 says
Wonderful article full of very interesting info.
meganpratt27 says
These are great highly recommen
meganpratt27 says
UVs are great highly recommend!
B says
With UV being so new, it will be interesting the long term effects of running one.
tsartors94 says
Love my uv sterilizer. Makes the tank really clear.
Patrick Jennings says
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.
trevorpem10 says
I use UV and I love it… just let the tank cycle first before turning it on.
devon maynard says
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.
Victoria Joy Brewer says
Very interesting.
Victoria Joy Brewer says
I’ve never had any reason to run one but I may try it out in the future
Dallas T. says
I like the idea of using a up sterilizer — wish list!
devaji108 says
I have a pentair 40W going my my RS650P 1st trying one really looking forward to it.
pumas0511 says
Great information. Thanks
zadok jollie says
I have always wanted one but now I want one even more.
rpkneumann says
Thank you for the information. I use chemicals instead.
Tanner Funai says
UV Sterilizers can be useful. I always keep new ones on hand or hooked up to tanks in case necessary.
Tanner Funai says
UV Sterilizers are a great tool to utilize all the time or as needed.
Chris Montesione says
No BRS did as investigate on it.
Scott says
UV sterilizers should definitely be used from the start to help control pests and algae.
Jeremy Pryes says
I’ll buy one when they come down in price.
Leo says
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.
Leo says
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.
Leo says
UV keeps my water crystal clear!
ed.leslie says
Installed UV system because many long time reefers recommended it.
Mark says
I have one running in my 125 Dt and sump. It a better way to help run your reef
Eric Brown says
They seem great except for losing you photo and other pods.
jason.kkemp101 says
I love my UV, have my apex run it 4 hours in the a.m. and 4 hours in the p.m.
Larry Moore says
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.
Josh Stevens says
If need be they are a great tool.
Brad Biliter says
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.