Should You Use a UV Sterilizer in an Aquarium?

Keeping your aquarium clean is crucial for the health of your fish.

It’s important that you provide the inhabitants of your aquarium with a great environment to live in if you want them to thrive.

One great way to keep your aquarium environment clean is by using a UV sterilizer. UV sterilizers are effective in getting rid of harmful bacteria, algae, and other nuisances like parasites. It can be a great addition to your fish tanks, working as both a prophylactic as well as a safety aid for your fish.

A UV sterilizer can be used both in freshwater and marine fish tanks.

Moreover, it makes the water crystal clear, so your aquarium looks even more attractive.

UV sterilizers have been proven effective in controlling infections inside the aquarium as they inhibit microbial growth, as well as free-floating algae.

But the best part is that the device neither kills the fish nor does it have any after-effects that might affect the fish.

Even though they are now widely used, the subject of UV aquarium sterilizers is still debatable as a lot of information on it is user-based.

This article covers everything you need to know about aquarium UV sterilizers.

What Is a UV Aquarium Sterilizer?

A UV sterilizer is basically a tube that emits UV light – a germicidal fluorescent lamp.

The lamp produces light with a wavelength of about 254 nanometers.

The water inside the aquarium is pumped through a sleeve made of quartz crystal, and it’s made to pass through high-intensity UV light.

There is an opaque cylindrical container that covers the device to stop the UV light from reaching the rest of your tank.

Every time water (with algae/ bacteria) passes over the bulb, it is irradiated with this wavelength.

As the UV light penetrates the algae or bacteria, it causes a mutation in the DNA (disrupts the genetic material inside the bacterial or algae cells). As a result, it stops their growth or multiplication in the water.

Therefore, UV sterilization is an effective way to control disease outbreaks in your aquarium.

They make sure that bacteria, viruses, and parasites are killed before they can infect your fish.

There’s no doubt that UV light is dangerous and cancer-causing but when the UV sterilizer is used cautiously and correctly, it will not be life-threatening for you or your fish.

Benefits of Using a UV Aquarium Sterilizer

The primary reason why UV sterilizers are widely used is that they are a convenient and effective option to improve the health of your fish tank by killing harmful bacteria, viruses, algae, and parasites.

These microorganisms pose a great risk of causing disease, putting stress on your fish, and even killing them.

Therefore, if you don’t want to lose your fish, killing the root of the disease should be your top priority.

UV aquarium sterilizers make this possible by preventing the infections in the first place as they kill the pathogens before they can attack your fish.

UV aquarium sterilizers are also great at killing off algae.

Algal blooms can get uncontrollable really quickly, even if you’re adding algae eaters into your tank.

Fortunately for you, UV aquariums can save a lot of your money that goes into maintaining a fish tank during an algal bloom or disease outbreak.

Factors That Affect the Performance of a UV Sterilizer

Here are some of the factors that affect the effectiveness of UV aquarium sterilizers.

UV Light Penetration

If UV light is unable to penetrate the water, it will obviously be ineffective at its job.

Therefore, if there is higher turbidity in the water, it defeats the purpose of installing a UV sterilizer inside the aquarium.

In high turbidity conditions, the UV light is unable to reach the bacteria and algae to kill them.

This is why it’s recommended that the UV sterilizer is positioned in a way that it comes after the biological and mechanical filters in the aquarium so that the water reaching the sterilizer is free from any particulate matter.

Another factor that affects UV penetration is salinity. The UV light penetrates better in freshwater rather than saltwater.

Also, the cleanliness of the bulb or quartz sleeve is also important.

If the bulb or sleeve gets covered by a film or mineral deposition, the UV light coming out of it will be partially or fully blocked.

Therefore, you will have to clean the bulb or the sleeve regularly. Finally, the distance of the lamp from the water also plays a role.

The UV light will penetrate clear saltwater only to a depth of 5 millimeters.

The Size and Type of the Microorganisms

Theoretically, UV radiation can easily kill all bacteria, viruses, protozoa, and algae.

The general rule is that for larger organisms such as protozoa, a higher intensity of UV radiation is needed to eliminate them.

Smaller microorganisms like bacteria can be killed with much lower doses. But there are differences between various organisms of the same type as well.

Therefore, even with bacteria, there are some who would be more resistant to UV radiation than others and therefore requires a higher dose.

Bulb Wattage

If you’re looking to kill a specific type of microorganism, you need to check the bulb power.

This is because different types of bulbs would have different bulb power.

Bulb power is basically the amount of UV light produced by the bulb which is reflected in the wattage of the bulb.

Therefore, having a bulb with a higher wattage means that it will produce more UV light.

It’s also important to note that the germicidal fluorescent lamp or bulb deteriorates with age, and in most cases, the bulb will need a replacement every 6 months.

For optimal performance, you need to maintain a temperature of 104-110 °F. Lower temperatures will result in less UV productivity.

The Contact Time of UV Light

The longer the water is exposed to UV light, the higher the efficiency of the light in killing the microorganisms.

The contact time or the dwell time is affected by the flow rate of water and slow-moving water increases the contact time.

This makes it possible for the light to kill more bacteria and other organisms.

Another factor that influences contact time is the length of the bulb. So, a longer bulb ensures that the water is in contact with the UV light for a longer period of time.

The amount of time needed to have the whole volume of water in the aquarium pass through the sterilizer, also called the turnover time, is important too.

Since the sterilized water is continuously mixing with the rest of the water in the aquarium, it’s impossible to sterilize all the water in the aquarium.

The Temperature

To get the best results, UV light should be produced at a temperature range of about 104-110 °F.

Operating them at cooler temperatures will compromise their performance.

A quartz sleeve around the bulb is effective in insulating it from the cool aquarium temperature and helps in maintaining optimum UV output.

It further protects from the harmful effects of UV radiation on the aquarium inhabitants.

What are the Limitations and Potential Side Effects of UV Aquarium Sterilizers?

While they do offer several benefits in terms of maintaining aquarium health, UV sterilizers are not a replacement for good biological and mechanical filtration, proper control of the nitrogen cycle, and regular water changes.

They can be ineffective in case there’s an algae infestation or other such nuisances that involve disease-causing microorganisms that are not freely moving in the water.

If you’re planning to install a UV sterilizer in your aquarium, there’s one thing you need to keep in mind.

It should not be used when you’re cycling the aquarium for the first time as that may kill the beneficial bacteria before they inhabit the gravel or bio-media.

Medicinal products are susceptible to UV degradation.

Therefore, you need to turn off the UV sterilizer when using the medication in the aquarium, especially chelated copper treatments.

The UV light breaks down chemical bonds inside the chelating agents, and that can result in an abrupt rise of copper ion concentration inside the aquarium.

UV sterilizers can be used to control parasites, but the required flow rate is so slow that it makes it unworkable on larger aquariums unless you use very high wattage UV systems (40 W+).

One more thing that needs to be taken care of is the temperature of the water.

UV sterilizers can heat the water as it passes through it, especially larger units.

Therefore, a chiller may be necessary to maintain the aquarium water at an appropriate temperature.

Should You Use a UV Aquarium Sterilizer?

UV aquarium sterilizers are very helpful in maintaining a healthy environment.

However, you cannot use them to replace mechanical and biological filtration and nitrogen cycle maintenance.

They work as an effective adjunct to necessary aquarium maintenance mechanisms.

They are completely safe to use when installed properly, and if you follow a proper maintenance schedule.

Those of you who are struggling with frequent aquarium disease outbreaks or algal blooms should definitely consider installing a UV sterilizer in their aquariums.

How to Maintain UV Sterilizers

You will have to check the quartz sleeve monthly and clean it with rubbing alcohol.

There are some larger UV sterilizers that have wiper mechanisms installed for more convenient maintenance.

You will also have to replace the UV bulb after 6 months of continuous use. Make sure you go through the manufacturer’s guidelines about this.

While installing or changing the bulb, don’t look at it directly when the unit is turned as that can damage your eyes permanently.

Always turn the power off when you’re performing maintenance to protect yourself against possible shock.


We hope that by now, you have a good understanding of what a UV sterilizer it and how it works.

This device can come in handy if you’re looking to keep your aquarium free of bacteria and algae.

In the long run, these UV sterilizers actually prove to be good investments as they increase the longevity of your aquarium and its inhabitants.

They are also easy to install and to look after.

You may also like the following articles about aquariums: