UV Sterilizer Uses and Purposes in Aquarium

UV Sterilizer Uses and Purposes in Aquariums

Do We Need to Use UV Sterilizers?

It is common knowledge that aquariums are susceptible to algal blooms, parasitic invasions and spread of pathogens regardless of proper aquarium cleaning practices and filter maintenance activities, hence a call for an additional cleaning back-up.

As surprising as this may sound, in some cases, mere cleaning and regular filter maintenance may not be enough to effectively tackle this problem, therefore you may consider the installation of Ultraviolet (UV) sterilizer in your tank to make your life easier.

UV sterilizers can be a great addition to any kind of aquarium. It will target even minute free-floating microorganisms present in the tank water and render them useless. On contact with a disease-causing organism e.g. bacteria, the radiation emitted by the ultraviolet light will alter its genetic material.

This goes further to shorten the organism’s life span and impede on its ability to reproduce. That way, there’s little chance of encountering algal blooms and further spread of disease in the aquarium.

Combating the outbreak of algae, bacteria, and other harmful microbes can be quite challenging especially for beginners in the hobby. These microorganisms will ruin the water quality and also make life unbearable for the tank inhabitants if they are not eliminated.

Now, regarding the main question. I would say that UV sterilizers do benefit our tanks to some degree. Therefore, if the budget allows, we should try them. However, I cannot say that they are absolutely a must-have tool. They also have some downsides that you need to know. So, keep reading for more information on UV sterilizers use and purpose in aquariums.

UV Sterilizers – Preventive Tools

You should note that the addition of a UV sterilizer is not a corrective measure but more a preventive one. The addition is more like an extra layer of protection to your aquarium, its function will be greatly aided by routine water changes and proper filter maintenance.

Also, another thing you should be aware of is that the UV light targets only free-floating microorganisms in the tank water, whereas microorganisms and parasites latching onto the body of fish, corals, substrate, plants, and decorations will not be targeted since it is not within the range of contact.

The Ultraviolet sterilizer should only be installed after your biological or mechanical filtration. Furthermore, be sure to control the flow rate through the filter in accordance to the manufacturer’s recommendations.

The essence of adhering strongly to these recommendations is to ensure that the UV sterilizer works optimally; with a focus on eliminating microorganisms and not the debris in the tank water, this also guarantees that the sterilizer has the appropriate amount of exposure time to eliminate the identified threats. Be sure to follow the guidelines for easy installation and usage.

UV sterilizers are readily available in a variety of models and configurations tweaked specifically for optimal efficiency. It is now left for the user to choose the one that best suits his aquarium system and needs.

UV Sterilizer Styles

UV sterilizer exist in two styles; we have the in-line UV sterilizers and hang-on UV sterilizers, and they are both made to effectively control the outbreak of disease-causing microorganisms in the aquarium.

–         In-line UV Sterilizers

The in-line UV sterilizers vary from its counterpart in terms of the placement style; in-line sterilizers are meant to be placed directly to the main filtration system.

This UV sterilizer is ideal for large aquariums, it should be installed after the mechanical filtration unit as the last in-line device before water is introduced.

–         Hang-on UV Sterilizers

Hang-on UV sterilizers are compact sterilizers that are mounted directly to the back of the tank. Unlike in-line UV sterilizers, they function as an independent device fed by a submerged powerhead. There are some hang-on UV sterilizers that may be connected to the return line from a canister filter or in-line filtration systems. Due to the easy installation and low maintenance requirements of hang-on UV sterilizers, they are more suited for smaller aquariums.

Ultimately, all UV sterilizers require a water or circulation pump and plumbing (PVC tubing) to transport water from the aquarium, through the UV chamber, and back into the aquarium.

Uses and Purposes of UV Sterilizers

  • UV sterilizer improves the overall health and cleanliness of your aquarium by targeting even the smallest of microorganisms and keeping their activities at bay.
  • It helps to get rid of disease-causing organisms before they can get to your shrimp, fish, corals,
  • UV sterilizers can tackle green cloudy water problems often encountered in fish tanks. As duly observed; the presence of UV sterilizer will help to transform green water to clean, clear water which the inhabitants love.
  • UV sterilizer effectively reduces the chances of possible algal blooms by making sure that the tank water stays clean and devoid of murkiness. 

How Do UV Sterilizers work?

UV sterilizer employs a germicidal fluorescent lamp that produces light at a wavelength of approximately 254 nm (nanometres). It works in a unique way that the water which carries harmful free-floating bacteria, algae, and other microorganisms passes over the bulb and is irradiated with this wavelength.

Going forward, mutation of the genetic material of the microorganism occurs as soon as the UV light penetrates it, this eradicates further growth and proliferation of the organism.

Factors that Influence the Effectiveness of UV Sterilizers

  • Size and type of the organism
  • Wattage
  • UV penetration
  • Contact / dwell time
  • Temperature

Size and type of the organism:

It is an established fact that ultraviolet radiation will eliminate bacteria and other disease-causing organisms. However, because of the size, larger organisms such as protozoa (Vorticella, Cladogonium ogishimae or Ellobiopsidae, etc.) demand a higher dose of Ultraviolet radiation than smaller microorganisms like bacteria and viruses.


In simple terms, the amount of UV light produced by the bulb is reflected in the wattage of the bulb. Bulbs with a higher wattage will produce more UV light and as the bulb ages, its ability to produce UV light will decrease. Hence the need to replace the bulb after 6 months of continuous use so that it will maintain the best performance.

UV penetration:

The ability of the UV light to effectively penetrate the tank water is highly dependent on a lot of factors.

Firstly, the UV light’s ability to penetrate is influenced by the clarity of the tank water. That is why it is essential to install UV sterilizers after biological and mechanical filters so that the water would be clear when it makes its way to the sterilizer as this ensures the best results.

Secondly, salinity also affects UV penetration, this is quite evident because UV light penetrates freshwater better than saltwater.

Lastly, the cleanliness of the lamp or its protective sleeve also matters. In a situation whereby the lamp or quartz sleeve is engulfed by dirt or film, the light will be blocked and this will minimize the UV light’s effectiveness.

Contact time:

The contact time is affected by the flow rate if the tank water, slower flow rates increases contact time and vice versa.

It should be known that the more contact time microorganisms get with the UV light, the more thoroughly it will eliminate them. Also, the turnover time is another determinant, this is the amount of time it takes to have the entire volume of water in the tank pass through the UV light chamber.


Ultraviolet light is best produced at a temperature range of 104 – 110 °F (40 – 43 C), and cooler temperatures translate to less output.
However, the protective (quartz) sleeve insulates the bulb from the cooler water and this enables it to maintain the proper output of UV light.

Choosing the Best UV Sterilizer for Your Aquarium

This hugely depends on your target or tank concerns as different microorganisms require a different amount of UV light to get rid of them.

For example, if your tank has a green water problem, then a cheap clarifying UV sterilizer can be of help. However, if your tank is plagued with algal blooms, bacteria, or protozoa outbreak, then you will need a more expensive UV sterilizer with a high wattage which will provide the best dwell time to kill them off.

UV Sterilizer Uses and Purposes in Aquariums typesAlso, the UV sterilizer must be matched to the proper flow rate in order to provide an efficient kill dose for the disease-causing organisms. This is the reason why most manufacturers provide a table that states the maximum tank size and appropriate flow rate for the models they produce.

Moreover, you need to put the size of your tank as well as the wattage of the bulb into consideration as they all have an impact on sterilization efficiency. There are a wide variety of UV sterilizer models to choose from, depending on metrics like wattage, flow rate, diameter of UV chamber, transmittance, and lastly, price!

Some popular models (links to Amazon):

AA Aquarium Green Killing Machine 3 Watt | Internal UV Sterilizer System with Power Head
COODIA Internal Green Water Killer Filter Aquarium Tank
Coralife BioCube UV Sterilizer for Aquarium, Mini

Limitations and Drawbacks of UV Sterilizers

  • UV sterilizers cannot function as a conventional aquarium filter. Therefore it should not be considered as a replacement for biological and mechanical filtration and routine water changes.
  • The device is not effective against algae or other disease-causing organisms that are not floating freely in the water column. It won’t eliminate algae and other pathogens attached to the glass, substrate, plants, or even fish.
  • UV sterilizer should not be used during the first cycling of an aquarium, else it may kill beneficial bacteria before they can attach to the bio-media or hardscapes. Therefore, it is recommended to install the UV sterilizer when the aquarium is already cycled.
  • The UV sterilizer should not be turned on when using medications in the tank. Otherwise, the active compounds present in it will be rendered inactive by the UV light.
  • UV sterilizers may heat the tank water as it passes through. This occurrence is most common when the UV sterilizer is larger than necessary for the tank size. In this case, an in-line chiller may be installed to help keep the aquarium water at the appropriate temperature.
  • They will reduce the chances and speed of contamination if there is an outbreak. They DO NOT guarantee 100 % efficiency.
  • UV sterilizers are safe for tank inhabitants: fish, corals, and invertebrates. Anyway, you should be aware that it may stress them a bit, but it won’t kill them.
  • They are quite expensive to purchase, there are models that cost as much as $500!

How to Maintain UV Sterilizers

To ensure that the UV sterilizer continues to function at an optimal level over time, the UV bulb will need to be replaced after 6 months of continuous usage. This bulb can also be changed in accordance to the manufacturer’s recommendations. So endeavor to look out for specific instructions regarding the replacement schedule if any.

Avoid making direct eye contact with the bulb when it is turned on. When installing or replacing the UV bulb, ensure it is turned off to prevent permanent damage to your eyesight.

In addition, cleaning the quartz sleeve should be an integral part of the maintenance culture. The Ultraviolet light will be less efficient when it is clogged with dirt or debris. So the sleeve needs to be checked monthly, detached, and cleaned properly (some manufacturers will include cleaning tools for this purpose).

Replace faulty parts by carefully dismantling the unit and removing the spoilt/expired part for replacement. Always ended the sterilizer is turned off throughout the repair or maintenance process.

In Conclusion

The goal of tank maintenance is to provide a clean, healthy, and stable living environment for the inhabitants in order to guarantee their growth and survival. Over time, the combined efforts of feeding, fertilization, and activities of tank inhabitants will result in the deterioration of the tank water, hence the need for filtration and routine water changes.

Moreover, the addition of new animals, plants, and decorations without proper quarantine practices may introduce disease-causing organisms into the tank water.

These problems all point to the importance of having a UV sterilizer installed in some situations. This supplementary cleaning device will increase the chances that the tank water stays clean, and at the same time. It will kill off some algae and other microorganisms that wreak havoc in the aquarium.

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