What Size UV Sterilizer Do I Need? (Complete Guide)

In this comprehensive guide, you will learn the proper size UV sterilizer you need for your saltwater aquarium.

what size UV sterilizer do I need

I will cover the following.

  • How to choose a UV sterilizer
  • UV sterilizer vs tank size
  • Types of UV sterilizers
  • UV sterilizer maintenance
  • And much more

Choosing a UV sterilizer for your saltwater tank is a big decision. There are several different factors that come into play. Type, size, cost, brand, are important to consider.

One of the most limiting factors you will need to decide on is size. What size UV sterilizer do you need for your saltwater tank?

I mentioned in the article how to set up an aquarium UV sterilizer, how important it is to choose the right size UV for your tank.

Let’s look further into the relationship between UV sterilizer size and tank size to determine the proper one for you.

How To Choose A UV Sterilizer

First, let’s answer a commonly asked question. Do you need a UV sterilizer? No, you don’t need one but they are very beneficial to have.

When choosing a UV sterilizer for your tank, first decide on the type to use. You will have 2 options to choose from. The hang on the back type and the inline type.

The hang on the back type is designed to hang on the back trim of your tank. They will include the mounting bracket, suction cups, and any other pieces needed to secure the unit to the tank.

For example, the Coralife Turbo Twist includes the proper mounting bracket that makes it easy to install onto the back of your tank.

The inline UV sterilizer is designed to be plumbed into your existing filtration system. These are perfect for tanks with sump systems or canister filters.

Once you decide on the type of UV sterilizer for your tank, you need to determine the size. This will depend on 2 factors. The size of your tank and the purpose you will be using it for.
Manufacturers will give you the rating and tank size that the unit is to be used for. The most common use for a UV sterilizer is for eliminating bacterial blooms and parasites in the water.
So you need to look at your tank size and UV wattage to determine the proper size. Also, consider the flow rate through the unit as this will be different for each model.

For example, the Coral Life Turbo-Twist manufacturer recommends the following:


  • 3x (9W) – up to 125 Gallons
  • 6x (18W) – up to 250 Gallons
  • 12x (36W) – up to 500 Gallons


  • 3x (9W) – 100-200 gph – 1/2″ or 5/8″
  • 6x (18W) – 200-400 gph – 5/8″ or 3/4″
  • 12x (36W) – 400-1200 gph – 3/4″ or 1″

If you don’t have the manufacturer’s tank size rating, you can use the following as a general guide.

  • 4-8 watt UV light for use up to 40-gallon tank size
  • 12-15 watt UV light for use up to 90-gallon tank size
  • 20-40 watt UV light for use over 100-gallon tank size

These numbers will provide you with the proper size UV to help eliminate bacterial blooms and cloudy water.

How long does a UV sterilizer take to work?

First, let me say that you don’t need to run a UV sterilizer 24/7. Once your reason for running it is accomplished, there is no need to keep it running all the time. If you are trying to clear a cloudy tank or take care of a bacteria bloom, once the tank has cleared, you can turn the UV off.

UV light will only be effective on free-floating organisms, so anything attached to the glass, rock will not be affected. Normally a UV sterilizer will be effective within 24-48 hours. You should see a huge improvement in your tank. Sometimes it can take 3-5 days depending on the issue at hand.

If you are using the UV to kill parasites, keep in mind that they are not always in the free-floating stage. For example, ich may take longer to eliminate as it’s not always suspended in the water column.

Marine Depot Aquarium Supplies

The Truth About UV Sterilizers In Aquariums

There is a lot of information online about the use of UV sterilizers in aquariums. Some of it can be quite confusing and difficult to understand. The complicated science with respect to bacteria, microorganisms, microscopic debris in the water, etc… is just way over my head.

But I have some information about UV sterilizers and aquarium use that makes a bit more sense and helps you understand the truth about UV light and aquarium use.

First, your aquarium water is packed full of millions of algae cells, bacteria, and other microscopic life. Even though we can’t see them, they exist. Most hobby grade UV sterilizers will help control bacteria and parasites but not eliminate them entirely. This would take a very expensive commercial-grade UV light that simply isn’t designed for aquarium use.

Research has shown that UV light in aquariums will help reduce the population of suspended organisms. In order for these organisms to be killed, they need to be exposed to a certain strength of light for a certain amount of time. It is very easy for microorganisms to not come in contact with the UV light and simply keep populating in your tank.

So UV sterilizers don’t completely sterilize your aquarium water. They simply help reduce the population density of microorganisms.

For the most part, using a UV sterilizer on your tank is beneficial for clearing cloudy water and bacteria blooms that cause green water. They can also be effective for parasites if in the free-floating stage, but research has shown that disease outbreaks were not reduced.

On an aquarium, it’s important that the proper size UV sterilizer is used in order for it to be effective. An undersized UV won’t do the job and you will be disappointed with the results. Always make sure the wattage of the unit and the flow rate of water going through it is suitable for your tank size. Contact time with the UV light is crucial for its overall effectiveness.

UV sterilizer maintenance

In order to get the best performance out of your UV sterilizer, you should place it after the filtration on the tank. You should also ensure the water flow rate follows the manufacturer’s recommendations.

This will ensure the microorganisms have proper contact time or exposure to the UV light which will kill the nuisance.

Regular maintenance should include checking for leaks, ensuring the bulb is working, cleaning the case of the unit, and changing the bulb when required. You also want to remove and clean the pump periodically to ensure it continues to work properly.

Most manufacturers will recommend the time when a bulb needs to be changed. On average you should change the bulb every 6 months to 1 year.

Best UV Sterilizers For Reef Tanks

Here are my top choices for both hang on and inline UV sterilizers.

Aquafit Aquatics UV 24 watt (Green Killing Machine)

I recently purchased the AA 24 watt UV and I am super impressed with it. I am using it to clear up cloudy water in my tank and within 24 hours of installing it, my tank was crystal clear.

The unit comes well packed and includes everything you need to run it right away. It even includes the powerhead pump. No need to buy one separately like other units.

AA UV sterilizer 24 watt

For the price, the AA 24 watt UV sterilizer is the best option on the market. It’s easy to use, installs within minutes, and begins to work fast. They are also a popular seller and are trusted by many hobbyists for years. The bulbs are also cheap to replace and are easy to find.

The one negative about this unit is it takes up real estate in your tank. But on a larger tank, it’s not noticeable and you can tuck it away in the corner or behind some rocks.

The AA UV 24 watt sterilizer is available on Amazon.

Coralife Turbo-Twist

The Coralife UV sterilizer is another popular brand that is easy to set up and use. They are unique as they feature a unique twist flow design. This design will direct water flow more evenly through the sterilizer.

The benefit is the water will be exposed more to the ultraviolet light and improving the efficiency of the unit.

They can be used as a hang on tank or inline style and include the mounting bracket. They are very affordable and reliable. Available in a 9 watt, 18 watt, and 36 watt which is great for larger tanks.

The Coralife Turbo-Twist is available on Marine Depot.


When choosing the right size UV sterilizer for your saltwater tank, you need to check your tank size and the manufacturer’s ratings. If you have an aquarium under 100 gallons, then the Aquafit Aquatics and the Coralife will work for you.

Remember to check the flow rate as this is important for water contact time with the UV bulb and its overall efficiency. UV sterilizers are very beneficial for saltwater tanks and they are affordable to buy and maintain. If you have the option to purchase one for your tank, I recommend you give one a try, you will be impressed!