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Reef Tank UV Sterilizer Guide (Pros, Cons, & Install)

Image Credit: DrMMI via Reef2Reef.com
Image Credit: DrMMI via Reef2Reef.com

Reef Tank UV Sterilizer Guide (Pros, Cons, & Install)

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Saltwater aquariums can sometimes be challenging. Bacteria, parasites, algae, etc., can be challenging to solve. There are various ways to tackle these problems—some more effective than others. A UV sterilizer can eliminate these problems and produce crystal clear aquarium water.


UV Sterilizers can kill tiny organisms floating in the water column. Bacteria, parasites, and some algae fall into this category and can be kept under control by an appropriately sized UV sterilizer.

Is a UV Sterilizer Required for a Salt Water Aquarium?

UV sterilizers are regarded by most aquarists as optional pieces of equipment, although some swear by them and wouldn’t have a reef aquarium without one installed. They are great additions for many saltwater aquariums to improve water clarity and fish and coral health, but most reefers don’t use them for various reasons.

Here are some of the reasons why they aren’t more popular:

  • Confusion around what they do and how they work
  • The added expense of the hardware required
  • The added complexity to plumbing and controlling the flow rate through the unit
  • Increased overall maintenance due to the need to clean the sterilizer and regularly replace the UV bulb
  • The fact that many reefers succeed well without one

Pros and Cons of UV Sterilizers

The best way to know if a UV Sterilizer is suitable for you is to weigh the basic pros and cons. There is a lot of debate over the effectiveness of UV Sterilizers, so it is good to know the facts.

Pros:

There are a lot of benefits to UV Sterilizers that make them worth consideration:

  • UV Sterilizers can be an excellent way to clear up cloudy water and help keep it crystal clear.
  • UV Sterilizers can eliminate floating bacteria, parasites, and algae as it passes into the light.
  • Because UV Sterilizers are separate from the aquarium, they will only kill things that are small enough to float through it.
  • Beneficial bacteria that live in rocks and the sand substrate will be unharmed since they are attached to rocks and beneath the sand.

Cons:

UV sterilization in aquariums has its downsides as well. Here are the main issues:

  • Because UV Sterilizers only eliminate floating bacteria, parasites, and algae, they will not cure your fish of conditions such as Ich that it has already contracted, but it can help control the spread.
  • It can negatively affect some medications dosed into the aquarium water if the UV sterilizer is on while the medicine is added to the water column.
  • Adds to regular aquarium maintenance as the UV bulb needs to be replaced occasionally, and the quartz sleeve that protects the bulb sometimes needs to be cleaned.
  • The cost of a unit can be surprisingly high, although it isn’t unreasonable compared to other reef tank hardware.
  • Water flow needs to be controlled and monitored to ensure that organisms in the water column are exposed to UV radiation for the minimum amount of time and intensity.

How To Pick an Appropriately Sized UV Sterilizer

A reef tank UV sterilizer should turn over the entire volume of your aquarium 1.5 times per hour. 

To ensure your UV sterilizer can meet your needs, you need to ensure that the “effective” flow rate will equal 1.5 times your total tank and sump water volume.

The flow rate of water through the unit is essential to ensure the marine organisms such as harmful bacteria, algae spores, disease-causing parasites, protozoa, etc., are exposed to the UV radiation long enough to prevent their ability to reproduce.

UV Sterilizer Effective Flow Rate

The effective flow rate of a UV sterilizer is the flow of water, usually listed in gallons-per-hour, through the sterilizer. The effective flow rate is different depending on what you want to kill with the sterilizer. Microscopic organisms vary in size and require unique exposure times to UV radiation to effectively kill each one.

Protozoa typically respond better to lower flow rates and more dwell time, while algae are easily treated with higher flow rates and less dwell time. Most people will find that oversizing their UV sterilizer and lowering flow rate to increase dwell time gives them the best results.

Can a UV Sterilizer Be Too Big?

Aside from extreme cases, no. Generally, going with a larger UV sterilizer will not cause a problem. If you increase the size of a UV sterilizer to an extreme level, you may begin to have problems with heat being inadequately removed from the sterilizer, which may cause it to prematurely fail.

As you increase the size of UV sterilizers, you can increase their abilities, but the performance increases begin to drop until there is essentially no return on your additional investment. For this reason, you should attempt to reasonably properly size your sterilizer although oversizing some can be effective if your budget can support it.

UV Sterilizer Sizing Calculator

To be effective, it’s recommended that a UV sterilizer should have an effective flow rate 1.5x the total water volume of your system.

If you need help determining the true volume of your aquarium or sump you can use our aquarium volume calculator to sort it out.

How To Plumb and Install a UV Sterilizer

There are a few different ways to install a UV sterilizer into your aquarium plumbing:

  • Plumb in line with your return pipe
  • Add a loop off of your return pipe
  • Use a closed-loop with a separate pump and plumbing not connected to your main plumbing

Also, it is essential to note that you want the cleanest possible water entering your sterilizer to minimize contaminants dirtying the quartz sleeve protecting the UV bulb. This means plumbing your sterilizer in just before where your plumbing returns water back to your display tank or installing a closed-loop in the return pump area of your sump.

Plumb Inline With Your Return Pipe

Plumbing inline is the simplest solution but the least effective. The problem with this solution is that you can’t control the flow rate through your sterilizer independently of your overall aquarium turnover rate. Unless you have a very large sterilizer, the flow rate is probably too high to effectively eradicate larger protozoa. It will likely help with clarity and algae control.

uv sterilizer plumbed inline diagram

Add a Loop Off of Your Return Pipe

Adding a loop off of your return pipe allows you to include a flow-reducing valve and tune the flow to an optimal setting to maximize the efficiency of your sterilizer. It also means you won’t have the added expense of a separate pump if you were to not include it with your main loop.

You could also include a flow meter like the Neptune Apex FMK (Flow Monitoring Kit). With this tool, you fine-tune your flow to keep it within the optimal range.

uv sterilizer return loop diagram

Plumb a Closed-Loop

By plumbing in a completely separate loop that isn’t connected in any way to your main loop, you don’t have to factor in the main return pump flow, and you don’t have to worry about tapping into your existing plumbing.

This is an easier way to include a sterilizer into your system, but it will require a separate pump. If you purchase a DC controllable return pump to run tank water through your sterilizer, you can adjust the water flow with the pump instead of plumbing in a flow-reducing valve to pinch off some of the flow.

uv sterilizer closed loop diagram

What Does a UV Sterilizer Do In a Fish Tank

Ultraviolet radiation can help control several issues in a saltwater aquarium. First, they help keep your water crystal clear and fish and coral healthy. But what exactly are they capable of killing, and what won’t they kill?

What UV Radiation Will Kill:

  • Free-floating Parasites
  • Free-floating Bacteria
  • Free-floating Protozoa
  • Free-floating algae
  • Any other free-floating unwanted microorganisms

Here are some things that can cause cloudy water or negatively affect your fish and coral health. Running a UV Sterilizer will help ensure the clarity of your water and will stay crystal clear.

What UV Radiation Won’t Kill:

  • It cannot kill microorganisms living on coral or fish, whether beneficial or harmful.
  • Copepods, isopods, or amphipods.
  • Microorganisms residing in your rocks or substrate.

How long should I run my UV Sterilizer?

UV sterilizers should generally be run 24 hours per day, 7 days per week. However, there are times that you may want to turn off your sterilizer. Here are some times you might want to turn off your UV sterilizer for a while:

  • A UV sterilizer should be run during the initial nitrogen cycle of your reef tank.
  • Do not run your sterilizer if you have to administer medication to your fish. The medicine will float in the water and most likely be altered or weakened after passing through the sterilizer.
  • You should avoid running your UV sterilizer when excess debris will be stirred up and floating in the water column. This can cause the sterilizer to become dirty and lose some effectiveness.
  • There may be times when you have to add beneficial bacteria to your reef aquarium.

What is UV (Ultraviolet Radiation)

Ultraviolet radiation is just one of many wavelengths along the electromagnetic spectrum. Visible light, radio waves, and x-rays are some of the other wavelengths along the electromagnetic spectrum. Ultraviolet radiation is just outside the visible light spectrum. Ultraviolet is on the shorter wavelength end of visible light, and infrared is on the longer wavelength end of visible light.

Ultraviolet radiation is emitted from the sun and is the radiation that causes sunburn. It is a powerful electromagnetic frequency that damages microscopic organisms enough to prevent them from reproducing when exposed to strong enough amounts for a long enough amount of time. It does so by damaging their DNA and preventing them from multiplying.
Ultraviolet lightbulbs are often used for their disinfecting properties, and aquarium UV sterilizers are an excellent example.

electromagnetic spectrum

How do UV sterilizers work?

UV sterilizers should generally be run 24 hours per day, 7 days per week. However, there are times that you may want to turn off your sterilizer. Here are some times you might want to turn off your UV sterilizer for a while:

  • A UV sterilizer should be run during the initial nitrogen cycle of your reef tank.
  • Do not run your sterilizer if you have to administer medication to your fish. The medicine will float in the water and most likely be altered or weakened after passing through the sterilizer.
  • You should avoid running your UV sterilizer when excess debris will be stirred up and floating in the water column. This can cause the sterilizer to become dirty and lose some effectiveness.
  • There may be times when you have to add beneficial bacteria to your reef aquarium.

UV Clarifier Vs. Sterilizer

UV clarifiers are similar to UV sterilizers, but the key difference is their power. Clarifiers are not as powerful as sterilizers. Clarifiers will improve water clarity by causing organics to clump together, making it easier for them to either be filtered out or the clumps will settle out of the water.

Unfortunately, some small UV clarifiers are marketed as sterilizers. They aren’t large enough to properly sterilize micro organisms although they will cause the water to become clearer. This leads people to believe they are sterilizing the water when they aren’t powerful enough to do so.

Be sure and research your choice thoroughly before you make a purchase.

Final Thoughts on UV Sterilization in Reef Aquariums

Ultraviolet sterilization is a powerful addition for taking a reef aquarium to the next level of clarity and improving the health of fish and coral. It’s possible to get excellent results if you properly size your sterilizer to your overall water volume and ensure the flow rate is appropriate for optimizing the dwell time in the sterilization chamber.

It does require some added maintenance and an understanding of how it works to take full advantage. Understanding what it can do and what problems it can’t resolve is vital for setting expectations.

While many reefers are wildly successful without the addition of a UV sterilizer, others swear by the benefits they experience when using one.
If you have the budget and are willing to deal with a bit of extra maintenance and some additional plumbing, you’ll likely be delighted with the return on your investment.

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