Do You Need A UV Sterilizer For Saltwater Aquariums?

Do You Need A UV Sterilizer For Saltwater Aquariums?


This is a question that is often debated throughout the saltwater community. Do you need a UV sterilizer for saltwater aquariums?

The answer is no. You don’t need to have one. But are they beneficial to have or are they harmful? This is what I will answer today.

What are they and how do they work?


Here is the deal with UV sterilizers. Basically they are a unit that has a watertight compartment with a UV bulb inside. This bulb will kill any undesirable free-floating organisms that pass through the unit. Things like parasites, algae spores, and bacteria that can be harmful to your tank and cause bacterial blooms and cloudy water.

The UV bulb will kill any of these items before they re-enter your tank. The length of time the water has contact with the bulb directly affects its performance and effectiveness. For organisms to be killed by UV, they must be exposed to the radiation at a certain strength for a certain amount of time.

Therefore UV can be very beneficial as it aids in keeping your tank water crystal clear and healthy.

But the keyword here is free-floating. Anything that is not free-floating, the UV light will not get rid of. Which is a good thing because it won’t harm any beneficial bacteria that is in your rock or sandbed since they are not free-floating.

The issue is that the UV can actually harm microorganisms that are beneficial to corals. So is using a UV sterilizer worth the risk?

Well, it depends on what your purpose is for using one.


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Should you use a UV sterilizer on your tank 24 hours per day?


I don’t see a reason why you would need to run a UV on a non-stop basis. Once your desired reason for using it is complete, you can turn it off.

If your purpose is to eliminate a free-floating bacterial bloom for clear water, then yes you can run the UV continuously until that has happened. They work great for that purpose.

Also, UV light will not reduce or eliminate algae that are already growing on the glass or live rock. Hair algae and other types are not affected. So using a UV for that purpose will not be effective.


Using UV sterilizer for fish disease


Do You Need A UV Sterilizer For Saltwater Aquariums?


If you want to use a UV for fish disease such as ich, remember that it will only be beneficial in the free-floating stage. Which ich is not all the time.

A UV light will reduce the number of parasites in the water column, hence making it easier to treat an outbreak. It will be helpful in reducing the impact of the disease.

However, it won’t prevent or eliminate the disease. This is because the UV will kill free-floating microorganisms and ich is not free-floating in all stages of its life.Do You Need A UV Sterilizer For Saltwater Aquariums?

What size UV sterilizer should you use?


The size of the UV unit you will need depends on your tank size and the purpose you need it for. As mentioned, it is most common to use the UV for bacterial blooms and keeping your water clear. For that you should look at the wattage and your tank size.

  • 4-8 watt UV light for tanks up to 40 gallons.
  • 12-15 watt UV light for tanks up to 90 gallons.
  • 20-40 watt UV light for tanks over 100 gallons.

Keep in mind that the life of the bulb being used will diminish over time. All UV bulbs will need to be replaced after 6 months.

Marine Depot Aquarium Supplies


The bottom line with UV sterilizers in a saltwater aquarium is that they are not required but some people find them useful. It really is up to you to decide if they will be beneficial to your tank.

Some hobbyists believe they are a waste of money and don’t help at all and some think they are a great investment and won’t have a tank without them. I am somewhere in the middle.

I do believe they can harm beneficial micro-organisms in the water column that are beneficial to corals. So if you have a reef tank, you need to be cautious. But for clearing a cloudy tank and ridding the tank of free-floating organisms, they will help.

There are alternative methods for keeping clear water in your aquarium like using activated carbon, filter padding, proper tank maintenance, and water changes.

For smaller tanks, UV sterilizers are not expensive. But if you have a larger tank, expect to spend a few hundred dollars for one. Here are my recommendations:

AA Green Killing Machine 24W UV

Coralife Turbo-Twist UV

Aqua UV Advantage 15W UV