AQUARIUM LIGHTING DIGEST

By Carl Strohmeyer

From the full article: AQUARIUM LIGHTING; FACTS & INFORMATION

Aquarium Lighting Overview

When choosing lighting for your aquarium (especially Reef or Planted Freshwater), there is much more to consider than watts per gallon.
The 2-6 watts per gallon for a reef or freshwater plant aquarium, less for fish, more for many corals; is a VERY basic start but that is very general and quite out dated due to the variety available modern lights with varying lumens per watt lights, different wavelength, focused lumens, PAR output, etc..
Unfortunately the watts per gallon “rule” is still thrown around today despite all the technological advances in lighting which often makes this grossly inaccurate (please read the full article to understand why the Watts per gallon is only part of the equation).
For a better understanding the full aquarium lighting article explains that a watt is simply a measurement of energy NOT light output or even quality. Even comparable lumen output at the lamp is no longer a good measure of lighting parameter performance due to focus and restrike (as well as PAR & related useful light energy); a good example is a modern LED (such as the Aqua Ray) which has a vastly higher useful lumen output than a comparable wattage CFL (such as a Current USA Compact Fluorescent) at 20 inches.

Another note with freshwater plant light requirements is that the 3-4 watts per gallon general rule applies to medium to high light plant requirements, not low light such as Java Moss, or in the case of Reef Aquariums stony corals such as Acropora.

Important Parameters to consider when choosing a light for your aquarium (not a complete list):

• Watts per gallon,
• Lumens per watt
• Lumen focus (AKA Restrike)
• PAR (often easiest determined by Kelvin output),
• Useful Light Energy (not wasted in yellow/green light spectrum that green plants and zooanthellic algae reflect)
• Output in relation to bulb length (this is where LEDs and to a lesser extent T2s and T5s excel).
• Lux, I generally only consider this parameter in deeper Reef and occasionally deeper planted freshwater aquarium to determine if I am getting the proper light where it needs to be.

Although still a popular measurement, the watts per gallon is part of the lighting equation as stated above is highly inaccurate when taken by itself. Taken together, the first FIVE points are the most critical (which does include watts per gallon), but no one of these should be a sole determiner of the lights.

As an example of the inaccuracy of the watts per gallon so-called rule, please consider these comparisons for an assumed 25 gallon aquarium:
* 20 watt T12 light with a Kelvin temperature of 5000 K,
Compared to a:
*20 Watt New Generation LED with an adjusted Kelvin temperature of 6500 K.

So assuming you would like 4 watts per gallon (this “rule” came about when T12 & T8 were the most common lights), you would need five of the described 20 watt T12 lights.
HOWEVER, once the other important factors are applied the described LED is shown to require vastly less wattage to produce similar results than the T8/T12 bulbs.
*PAR; the LED is more than 25% higher, as well many current LED emitters designed for aquarium and plants are more than 50% higher.
As well the useful light energy adds at least another 25% for an increase of 50% in this area of light output
*Focused Lumens; the LED 166% more efficient in focused lumens (about a 2/3 reduction of necessary watts)
*Lumens per Watt; the LED is double the lumens per watt.

In a rough math equation using a starting point of 100% of the T8/T12;
100 less 75%= 25% less 67% (2/3) = 8.25% less 50%= 4%
In other words you would need 4% of the wattage to provide the same lighting as similar watt fluorescent aquarium light
This would roughly result in just one (actually less, and you will still have more light) of these lights for the same tank size (a 25 gallon in this example).

As you can see the watts per gallon rule falls apart in this comparison, in fact in this comparison one watt of high output emitter LED has a higher output of usable light than the 25 watts of the T12 (100 divided by 4). Of coarse the differences can vary, so even this comparison only works for the described lights and tank, this is also based on the newer Cree XR-E Power LED emitters employed by TMC which have a high output of useful energy.
Even with Metal Halide, tests have shown that a high output 12 watt LED can out perform a comparable 175 watt Metal Halide (although this is raw data and after considering water penetration a safe assumption would be 12 watt comparable Kelvin HO LED = a 100 watt comparable MH).
Bluntly, the new generation Cree XR-E Power LEDs are brightest lights per watt.

Changing bulbs:
With the exception of LED, most aquarium bulbs go through what is called a half life whereby they are at 50% output. This generally happens around 6 to 9 months in time with normal usage however with lower usage (say 8-12 hours per day) this can be stretched to 12 months plus.

Lighting Time
Here is a summary of lighting requirements for different aquarium types. I recommend timers for any aquarium to provide good daylight/night cycles, however this is even more important with Planted Freshwater and Saltwater Reef or Nano Reef tanks. Turn the actinic lights on about one to 1/2 hour ahead of the daylight bulbs and one to 1/2 hour later in the evening. I generally have the brightest lights on for about 12 hours per day. Sometime with MH I will have them in a third cycle that is on for only abut 10 hours or less. I would run moonlights for about 14-16 hours (some prefer to run these 24/7, however I have yet to find in benefit from this that can be scientifically proven other than aesthetics).

Light (lamp) placement:

Pendant vs. MirrorThe advantage to a pendant reflector over a mirror (depending on reflection quality) is that it will radiant downward in a slightly more magnified fashion than a mirror, however the mirror has one advantage over the pendant and that is more wide spread light distribution.
So this choice comes down more to tank arrangement of plants or corals.

Light Penetration
What is often a bigger issue, especially with deep tanks (over 24 inches) is to allow as much of the blue light (which is found as part of the light spectrum of high PAR Daylight 6400 K lights) as possible through to the tank and often a glass top will block these light rays (over 60%) so using polycarbonate or no lid at all may do more for effectiveness than whether you use a mirror or pendent (see further in this article for more on this subject).
As well for tanks over 24 inches the use of some higher Kelvin in your light “mix” may be necessary for coral tanks or in some cases high light requiring plant tanks. The use of 14,000 K MH in a mix with High PAR 6400 K SHO lights may provide the “mix” necessary for deeper tanks. Even in tanks under 24 inches, the use of actinic blue lights may help provide the correct PAR to specimens lower in your tanks water column; a LED light strip may help provide this.

Specimen Placement
One more point is depending on what you are using your light for (especially a high output light such as a MH. LED or SHO), I would move corals as high up in the water column as possible, this especially important with SPS corals (short polyp stony corals) where placement on the rocks directly under your lights is even more essential. This is not as essential with LPS corals (long polyp stony corals) since they are more commonly found in sandy lagoon bottoms.
If this light is for Freshwater plants I would move the high light requiring plants directly under the lights (or even elevate them with terracing, which can look quite attractive if done well and serve a dual purpose of aesthetics and better light energy absorption).

TANK SET UP LIGHTING SUGGESTIONS:
As a guide I will make a few suggestions in the following sections, however please take these as suggestions, not something written in stone. Please consider the more in depth article referenced for this summary article, your personal aquarium parameters, inhabitants, budget (which is always important), & more when deciding what lighting systems or combinations there of to use.

• A BASIC FRESHWATER FISH TANK

*As an example, with a 36”L x 15”W x 16”H 40 gallon aquarium I would suggest (2) 11 Watt 6400K (or even only one 13 watt) T2 Lights as a good set up for a basic freshwater aquarium.

For further basic freshwater tank lighting information, please see this article (in the Light Basics section): “Freshwater Aquarium Basics, Care”

• A FRESHWATER PLANT aquarium needs more ultra-violet and infrared plus more lumens/watts of light. Photosynthesis takes place at the blue end and at the red end of the Nanometer curve (420 nm blue and 670 nm red). The “valley” is around 550 nm, this is where most visible light is present and is why plant leaves mostly reflect green light, while they absorb red and blue. This curve drops sharply below 400 nm and above 700 nm. This area of peak photosynthesis is referred to as “PAR” as discussed in the In Depth Aquarium lighting Article

*As an example, with a 36”L x 15”W x 16”H 40 gallon aquarium I would suggest (2) 13 Watt 6400K T2 Lights as a good set up for a low/medium light planted aquarium, Or (2) 65 Watt SHO or (2) Natural Daylight TMC LED lights for a high light planted aquarium (of coarse combinations of lights and other variables apply)

*Currently. the SHO is still my preferred light for high light requiring planted tanks over much over 60 gallons due to the shear output of usable light energy in a relatively small space (as well as based on results in the indoor horticulture industry). However these lights do not fit as well into low hoods as would a LED, T2, or T5 and and although they do not require fans, good hood ventilation is also important. The SHO also requires a little more DIY ability as well.

Please read this freshwater aquarium plants article for much more about this subject:
“Planted Aquariums”

• A BASIC SALTWATER or FOWLR tank also does not have as high of requirements, as but more than freshwater.

For smaller tanks the T2 or T5 make a good choice and the SHO for larger aquariums.
Finally and although pricey, an LED is still worth considering especially when you consider the 50,000 hour life, and high usable light energy output.
Recent research in humans can also be extrapolated to fish only tanks that shows good lighting can improve health and increase disease resistance; for this reason a T2, SHO, or LED are worth considering over a 1980s style “Marine Glo” T12/T8 light

*As an example, with a 36”L x 15”W x 16”H 40 gallon basic marine aquarium I would suggest (2) 13 Watt 6400K T2 Lights, or (2) 13 Watt 6400K and (1) Blue T2 Light as a good set up (other combinations of lights and other variables apply).

• A BASIC REEF OR NANO REEF:
The new 6400K, Actinic T-2 Lamps/Fixtures are good compliment to a Nano Reef due to their compact size and high lumens per watt output and our now my choice for these tanks. As noted in the in depth Aquarium Lighting Article, optimum PAR is what the coral needs and this is achieved best in lamps around 6400K, ESPECIALLY in smaller Nano Reefs!
These fixtures can also be mounted in parallel and/or snapped together end to end for larger aquariums with higher output needs.

Other considerations especially larger basic reef tanks are a VHO Light or even a 65-105 watt SHO bulb. The Helio bulbs come in actinic 50/50 combination for those still holding to the “old school” view that actinic is a must (albeit scientifically untrue!!!).

Of coarse the Metal Halide should never be over looked especially if your budget can afford them.
Finally the VERY new AquaRay LED Light systems can be used alone or in combination with T2 or T5, CFL or SHO lamps for Basic Reef or Nano Reef Tanks. (generally recommend the Aqua Ray combined with the T2 6400 fixtures in tanks under 60 gallons)

*As an example, with a 36”L x 15”W x 16”H 40 gallon aquarium I would suggest (2) Reef White TMC LED lights or (2) 6400 T2 & (1 or 2) Marine Blue TMC LED for a basic reef aquarium (of coarse combinations of lights and other variables apply)

• AN ADVANCED REEF with Hard Corals These corals need more energy to sustain themselves from light. (Hard corals are photosynthetic corals which obtain their primary source of energy from light and then also actively feed to obtain more energy.) Based on your setup with hard corals (not excluding other factors), I would recommend using one or multiples of the following lights: Metal Halide, Marine Reef LED (Reef White), SHO bulbs, T2, T5, or CFL bulbs. Please note that certain combinations work better for hard corals based on light attributes including PAR, Useful Light Energy, Lumens, Focused Lumens etc. The equations for these can be found in the Important Parameters Section of this article or for much more in depth discussion of these parameters see: “Aquarium Lighting Facts and Information”

A combination of a Marine Blue LED and 85 or 105 SHO lights can be an effective lighting system for many advanced reef tanks under 125-150 gallons. With this configuration, the best way to install these in your canopy/hood would be to place them in a slightly staggered parallel.

It should be noted that 6400K lighting is where you will find the closest output to optimum PAR that is required by the symbiotic algae that live within the corals.
The exception is that for tanks over 24-30 inches deep you will need a higher Kelvin output to achieve maximum PAR, usually 8000K to 14,000K to reach the bottom corals.

In a large Advanced reef aquarium combinations of lighting systems may yield your best results and also possibly alleviate the need for expensive and often unreliable chillers.
For example in an 8 foot 200 plus gallon advanced reef tank I would recommend the use of about four 85 or 105 SHO lamps mixed with a couple Reef White LED and open EcoSystems Metal Halides over the most sensitive corals.

For the full article (including Lighting Types and vastly more expanded & updated lighting information:
AQUARIUM LIGHTING; FACTS & INFORMATION

REDOX IN AQUARIUMS

Redox In Aquariums
From the full article: THE REDOX POTENTIAL IN AQUARIUMS (& PONDS); How Redox Balance Relates to Good Aquatic Health
By Carl Strohmeyer

Aquatic Redox Overview

Unfortunately this aquarium/pond parameter is Not a well known process among many aquarists, the implications of Redox for a healthy aquarium are quite far reaching, and thus important for any aquarist considering moving from basic aquarium (or pond) keeping to advanced to understand.
Redox, also known as Redox Potential, oxidation potential, & ORP (oxidation reduction potential) describes the ability for the loss of an electron by a molecule, atom or ion to the gain of an electron by another molecule, atom or ion. Without this ability to gain electrons many minerals cannot be absorbed and properly assimilated. So it is very important to keep a healthy Redox Balance via proper dissolved oxygen levels, UV Sterilization, and proper positively charged mineral levels (such as Calcium and Magnesium).
(Please click on the picture above/right to enlarge for a better view)

These three factors have the most affect in Redox Balance Maintenance in Aquariums
• Water Changes; this is the most obvious and simple, however this is often not sufficient and sometimes the new water used does not have adequate mineral ions (especially if RO water is used even in part), so supplementing with mineral replenishers (such as SeaChem Replenish, Wonder Shells, Instant Amazon, etc.) even during water changes may be necessary
• Addition of positive mineral ions in between water changes, especially during times of stress or high bio loads can increase the Redox Reduction to counter oxidative affects on fish
• Use of UV Sterilizer which impacts Redox Balance in a different way than water changes or additional minerals; the UVC irradiation destroys destructive oxidizers in the water column which can otherwise add oxidative stress to fish.

*Oxidation describes the loss of an electron by a molecule, atom or ion
Example: Redox processes such as the oxidation of carbon to yield carbon dioxide.

*Reduction describes the gain of an electron by a molecule, atom or ion.
Example: The reduction of carbon by hydrogen to yield methane (CH4).

Another example: Calcium or Magnesium which initially are composed of positively charged atoms immersed in a sea of movable electrons may have given up all possible electrons to cells under oxidation. It is for this reason, then, that calcium and magnesium supplies must be constantly renewed; without this “fresh” calcium, etc. your Redox balance will suffer. Think of it this way; a storage battery “works” only when a positive and a negative electrode are present to maintain an electrical current. When the positive plates become exhausted, the battery is no longer any good (even though the metal plates and other “ingredients” for the battery are still present; so it is that your GH or Calcium Test may show adequate minerals, but these minerals have been oxidized an thus rendering the test inaccurate).

The above are over simplifications of the process, so please read on as I will go into further depth as the article progresses, especially as Redox relates to aquatic health.

Oxidized Water:
Oxidized water with its Redox potential of +700 to +800 mV is an oxidizing agent that can withdraw electrons from bacteria and kill them. The oxidized water can be used to clean hands, sterilize utensils, and treat minor wounds.

Here are a few oxidizers: ozone (O3; Oxidation potential= +2.1), hydrogen peroxide (H2O2; Oxidation potential= +1.82), chlorine (Cl2) and chloramines (NH2Cl).

Reduced Water:
Reduced Ionized with a Redox Potential of -250 to -350 mV readily donates its electrons to unusual oxygen radicals and blocks the interaction of the active oxygen with normal molecules. Substances which have the ability to counteract active oxygen by supplying electrons are called scavengers. Reduced water, therefore, can be called scavenging water. Reduced water inhibits excessive fermentation by reducing indirectly metabolites.

Here are a few reducers, in other words, elements or processes that transfer electrons to another substance;
Magnesium, Calcium, Sodium, and the process of Photosynthesis involve both oxidation and reducing.

As one can see from the graph that elements such as most metals, as well as essential elements for aquatic life: Calcium and Magnesium are major reducers however because of this they are also most easily depleted (the elements at the top and the bottom of the graph are most easily depleted in their oxidation or reducing properties).

What is important to note, is that although oxidation is a necessary part of biochemistry for fish and all animals (such as for energy production), the normal healthy state is one of reduction. During normal biochemical processes molecules that are normally reducers give up their electrons (in much the same way a car battery does until re-charged), so without a recharging via the addition of new minerals that are high in these electrons or even processes such as UVC sterilization (or even high PAR lighting), your aquatic biochemistry will suffer and eventually so will your fish!

One more basic generalization to consider before reading the more in depth article is this: Water that is of low pH (acid), in general, measures high ORP while water of high pH (alkaline) measures low ORP. However, in natural water (generally spring water), acidity of minus ions and alkalinity of plus ions can coexist (more about this in Natural Redox).

It is important to note that Aquarium Redox can be a complex subject with some basic principles to also understand, however this is a subject that simply reading one section of this article will yield incomplete information. For this reason I recommend reading the whole article.

For the full article (including management & summary) please follow click here:
THE REDOX POTENTIAL IN AQUARIUMS (& PONDS);
How Redox Balance Relates to Good Aquatic Health

IRIDOVIRUS IN GOURAMIS

Iridovirus in Gouramis
From the full article: EDIS; Iridovirus in Gouramis
By RuthEllen Klinger, Ruth Francis-Floyd, John Slaughter and Craig Watson

What Are Iridoviruses?

Iridoviruses are a family of viruses (130–300 nanometers in size) that contain DNA as their genetic material and have an icosahedral (20-sided) capsid. Iridoviruses have been found in a wide variety of fish, including both freshwater and saltwater species. Some iridoviruses have been associated with serious diseases (e.g., viral erythrocytic necrosis of salmonids) while others have only been found in apparently healthy animals (e.g., goldfish iridovirus). One iridovirus causes a disease called lymphocystis which causes unsightly skin lesions on infected fish, but otherwise is of little consequence.

Iridovirus in Gouramis

An iridovirus was found in spleen and intestinal tissue of gouramis from the genus Trichogaster that were dying with signs of systemic disease. Mortality rates of affected fish have varied from low (0.5–10%) to moderate (50%) with death usually occurring 24–48 hours after the onset of signs. Clinical signs associated with the presence of the iridovirus have included darkening of body coloration and lethargy. Sick gouramis often stop eating and the abdomen may be distended. Internally, an enlarged spleen has been the most notable abnormality. The intestine may be reddened, and a clear amber fluid may be present in the body cavity. Laboratory examination for bacterial, fungal, or parasitic agents has frequently been negative. Through electron microscopy (EM), abundant iridoviral particles have been found in the spleens and intestines of dying fish.

An iridovirus has been isolated in cell culture and cytopathic effect (death of infected cells) has been observed. Although the iridovirus has been implicated as a possible cause of disease in gouramis, efforts to reproduce the disease under laboratory conditions have not yet been successful.

For the full article (including management & summary) please follow click here:
EDIS; Iridovirus in Gouramis
Further reference:
RuthEllen Klinger, Biological Scientist, Fisheries and Aquatic Sciences; Ruth Francis-Floyd, Associate Professor, Fisheries and Aquatic Sciences; John Slaughter, Veterinarian, Hillsborough County Extension Service; Craig Watson, County Extension Agent, Hillsborough County Extension Service; Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.

KOI POX; HERPES VIRUS

Koi Pox; herpes virus.
From the full article: Koi Herpes Virus (KHV) Disease

Introduction;

Koi herpes virus (KHV), a viral disease highly contagious to fish, may cause significant morbidity (sickness or disease) and mortality in common carp (Cyprinus carpio) (Hedrick et al., 2000; OATA, 2001). This species is raised as a food fish in many countries and has been selectively bred for the ornamental fish industry, where it is known as koi. Historically, the first outbreak of KHV was reported in 1998 and confirmed in 1999 in Israel. Since then, other cases have been confirmed in the United States, Europe and Asia (Hedrick et al., 2000; OATA, 2001; Anonymous, 2003). This information sheet is intended to inform veterinarians, biologists, culturists, and hobbyists about KHV.

What Is KHV?
KHV is currently classified as a DNA-virus belonging to the virus family Herpesviridae (i.e., a herpes virus). Although there has been some scientific discussion regarding the accuracy of this classification (Ronen et al., 2003), more recent work (Waltzek et al., 2004) shows strong evidence that KHV is indeed a herpesvirus, based on morphology and genetics. KHV disease has been diagnosed in koi and food fish carp (Hedrick et al., 2000; OATA, 2001). Other related cyprinid species such as the common goldfish (Carassius auratus) and grass carp (Ctenopharyngodon idella) seem to be unaffected by KHV. As with other herpes viral infections, KHV is believed to remain in the infected fish for life, thus exposed or recovered fish should be considered as potential carriers of the virus (OATA, 2001).
KHV disease may cause 80-100% mortality in affected populations, and fish seem most susceptible at water temperatures of 72-81°F (22-27°C) (OATA, 2001). This viral disease affects fish of various ages, but cohabitation studies show that fry have a greater susceptibility than mature fish (Perelberg et al., 2003).

What Are the Signs of KHV?
Clinical signs of KHV are often non-specific. Onset of mortality may occur very rapidly in affected populations, with deaths starting within 24-48 hours after the onset of clinical signs. In experimental studies, 82% of fish exposed to the virus at a water temperature of 22°C died within 15 days (Ronen et al., 2003). KHV infection may produce severe gill lesions and high mortality rates. In some cases, secondary bacterial and parasitic infections may be the most obvious problem, masking the damage caused by the primary viral infection. Behaviorally, affected fish often remain near the surface, swim lethargically, and may exhibit respiratory distress and uncoordinated swimming.

External signs of KHV may include gill mottling with red and white patches (see picture) (similar to Columnaris disease), bleeding gills, sunken eyes, pale patches or blisters on the skin. Microscopic examination of gill biopsies often reveals high numbers of bacteria and various parasites (Hedrick et al., 2000; OATA, 2001; Goodwin, 2003). Internal signs of KHV are inconsistent and non-specific, but they may include adhesions in the body cavity and a mottled appearance of internal organs (Hedrick et al., 2000; Goodwin, 2003).

How Do Fish Get Infected with KHV?
The herpes virus that is responsible for KHV seems to spread in the same ways as most herpes viruses. Methods of transmission include direct contact with infected fish, with fluids from infected fish, and/or with water or mud from infected systems. Depending upon water temperature, fish that are exposed and susceptible may become infected and either develop the disease and die or become carriers of the virus (OATA, 2001). Goldfish and other fish in the carp family are not susceptible to KHV disease, and they do not appear to act as carriers of the virus (Perelberg et al., 2003; Ronen et al., 2003).

For the full article (including treatment) please follow click here:
Koi Herpes Virus (KHV) Disease

UV STERILIZATION; UVC Irradiation

From the Article “UV Sterilization”

I am using this article for the first article digest as this seems to be an area of aquarium/pond keeping with much misunderstanding or even blatant misinformation.

Overview
Ultra violet sterilization is one of the most effective means of disease prevention in aquariums and ponds and for general water quality control in aquariums and ponds, which is part of where a properly installed UV Sterilizer helps provide improves a fish’ chances in fighting diseases such as ich that UV Sterilization is less effective directly in destroying. Part of the reason for UV Sterilization (which is often missed) is that the UVC radiation which is contained in the unit will break down oxidizers in the water column that would otherwise lower a fish’ immunity (Redox Balance), this aspect is often missed as many only focus on the germicidal/algaecidal properties of UV Sterilizers. Please read this article for more about this subject: “Fish Immune System and UV Sterilization”.

Benefits
There is a lot of new evidence as to the benefits of UV sterilization for ALL fish, and many myths have been dispelled such as “UV Sterilizers destroying beneficial nitrifying bacteria”. I will try and present material in as readable a format as possible, rather than get down to too much scientific jargon that is difficult for many to understand as many facts can often be presented without every technical term applied (although at times I may have too). I am also constantly researching this subject, so this article may not be the same article in three months, so please read on.

UV Sterilization is also effective for controlling suspended algae (green water) in ponds (along with proper filtration such as Veggie Filters/pressurize filters, please see this article: “A Clear Pond; pond information”)

UVs are also useful in Reef aquaria, especially new ones where the chance of disease introduction is high and the UVs help in keeping a balanced Redox Potential is useful. As the reef aquaria ages the sterilizer can be placed on a timer or turned on and off as needed.

As for the Redox Balance, this is an often overlooked aspect of both freshwater and saltwater aquarists. The Redox Balance is basically the oxidation and reduction properties of water. This is VERY important for proper breakdown of organic waste (the oxidation side of Redox)! Especially in aquariums where the fish/invertebrates come from waters of low turbidity (African Cichlids) or tend to produce a lot of waste (Goldfish).
Most experts now agree that the Redox should be +300 to -100 mV for marine or +125 to -200 mV for freshwater for healthy fish immunity, which a UV Sterilizer can help maintain,
For more information about the Redox Potential:
Aquarium Redox Balance

Anecdotal Arguments Against
One argument against UV Sterilizers in ponds is that they are not natural, but for the clarity most persons want out of their pond, this is not possible without either UV sterilization or a flow thru stream (although many persons with well planted, well shaded ponds do well with clarity).
Many articles I have read state that a UV is not that beneficial to an established aquarium as a healthy aquarium depends on beneficial bacteria typically growing on media in your filter which neutralize ammonia. Unfortunately the problem with this statement is beneficial bacteria belongs in the filter, not in the open water. Also this is great for advanced aquarists who are not adding fish and have a healthy Redox Potential/Balance, but not in the real world of average and above average aquarists that I have dealt with in the 100s of aquariums I have serviced.

Maintenance
UV Sterilizer maintenance is quite straight forward; make sure you keep your unit dry on the outside, if used for a pond try and protect your unit from harsh weather (most sterilizer can withstand the outdoor environment, they just last long if they can at least be partially sheltered).
Change your UV bulb every 6 months for aquariums, and also every 6 months for ponds in warm climates where there is no winter freeze. In cool climates a pond UV bulb can be changed every season (usually late spring/ early summer)

For the full in depth article “UV Sterilization”