Why Do I Need a UV Sterilizer?

In this guide, we explore the benefits of using a UV sterilizer in aquariums. It’s an effective tool for eliminating harmful bacteria, algae, and parasites, enhancing water quality and preventing fish diseases. We also covers different types of UV sterilizers, their installation, and maintenance.

Key points include the importance of matching flow rate for optimal efficiency and the fact that UV sterilizers won’t harm beneficial bacteria or fish. The guide also provides recommendations for various UV sterilizers suitable for different aquarium sizes and needs.

A UV sterilizer is a great filtration device used in aquariums to eliminate bacteria, algae, and other bacteria-caused diseases like Ich or microscopic parasites.

Using UV light to sterilize water before your fish can get sick is a preventative measure or an “insurance policy” for your fish tank. 

So, if you’re wondering whether you need a UV light to sterilize the water in addition to a standard filter, you’d be surprised by what an excellent addition a UV filter makes to your tank’s water quality. Here’s what you should know.

What Is UV Sterilization?

A UV sterilizer is a tube-shaped ultraviolet light that fits inside a water tube or filter tube, and as water passes through the light band, the UV light kills single-cell organisms by altering and damaging their DNA.

Direct exposure to ultraviolet light is dangerous, but when the UV sterilizer is used correctly and cautiously, it does not threaten you or your fish, invertebrates, or corals.

Technology Is Here to Help

UV sterilizers come in various types and shapes.

The costs of a UV unit can vary from $30 to several hundred dollars depending on the UV light’s power, water flow capacity, and the brand.

When choosing a UV sterilizer, you’d first have to decide where to fit it in your filtration system, what you require of the light, and what capacity UV sterilization you need for your water volume. 

For example, you might consider an entry model sterilizer if you own a small to medium fish tank and an extra large water flow sterilizer with multiple UV light bulbs for your outside pond.

We think you may be interested in the Best Fish For Ponds.

Type of UV Sterilizer

UV sterilizers for aquariums come in two main types: inline and hang-on. Inline sterilizers are integrated into the aquarium’s filtration system, while hang-on models attach to the outside of the tank. Both types use UV light to eliminate harmful microorganisms and maintain water clarity. The choice between these types depends on the aquarium’s size and setup.

Consult with the manufacturer or pet store about the type of UV sterilizer you need.

Most UV sterilizers are designed as a tube-like device with an in-and-out flow. Some clamp across your tank tube, sterilizing water before it returns to the tank.

However, a UV sterilizer can also work as a stand-alone device with its own water pump. It would then connect in line with a power head or connect to the outflow of your external canister filter. Some advanced filters include a UV light as part of the filtration process in addition to the traditional filtration media.

If you connect the UV sterilizer to your canister filter, ensure it is connected to the filter outflow to kill the excess bacteria, algae, and parasites that were not filtered from the water. This allows the light to work optimally by not wasting light on filtered sterilizing particles.

All UV sterilizers contain a UV light bulb (or more than one) that lasts up to 14 months before needing to be replaced.

It is important never to touch the bulb directly by hand because your bare skin can damage it. Wearing rubber gloves is a good idea to give you and the light some protection. Some lights can also cause an allergic reaction if the chemicals of the light come into contact with your skin.

Efficiency of UV Sterilizer

The efficiency of a UV sterilizer in an aquarium depends on matching the water flow rate with the UV sterilizer’s requirements. This ensures optimal UV light exposure to the water. If the flow rate is too high or too low, it affects the sterilizer’s ability to efficiently kill harmful microorganisms. It’s essential to follow the manufacturer’s recommendations for matching water flow power and UV light bulb power.

While UV light can almost instantly sterilize water, it requires a specific flow rate to clean the water of harmful bacteria optimally. So, your flow rate must match the UV sterilizer’s requirements to ensure optimal UV light exposure to each gallon of water.

If the water flow is too strong, the exposure is very short and might not efficiently kill the malicious microorganisms. Also, if the water flow rate is too slow, it may sterilize the bacteria, algae, and parasites, but the process will be time-consuming.

Always match the water flow power with the UV light bulb power according to the manufacturer’s recommendations.

UV Light Can’t Kill Beneficial Bacteria

UV light sterilizers can only kill bacteria that pass through the light area, so since the light is isolated on a water tube, it won’t kill bacteria not free-floating in the water. Beneficial bacteria tend to form colonies on gravel, rocks, wood, and plants and aren’t as likely to float in the water as algae and harmful bacteria.

Beneficial bacteria remain undisturbed unless some of it flows through the water and goes through the UV sterilizer because the beneficial bacteria live on gravel, rocks, wood, etc.

Install the UV sterilizer to function when the aquarium water cycles.

UV Sterilization Can’t Kill Fish

When installing the UV equipment, ensure you follow the manual, and if you have questions or difficulties, contact the company. UV sterilizers are safe for fish, corals, and invertebrates. There should be minimal stress on the fish from the light. As with eliminating microorganisms, the UV light won’t harm fish if these don’t swim into the water tube where the light functions. 

Never look directly at the light because UV light may damage your eyes. Never switch the UV sterilizer on when installing or working on it. Unplug all other devices from the fish tank when installing to protect these in case there’s a power surge.

After installing the light and other tank equipment, perform safety checks to prevent leaks.

UV Light Won’t Save Already Sick Fish

Fish that are already affected by illness caused by bacteria or parasites require medication to help eliminate microorganisms that have already compromised the fish. For the bacteria, algae, or parasites to die, they have to pass through the UV sterilizer, which means the contaminating bacteria already on the fish won’t be destroyed (as the fish can’t pass into the tube).

However, using the UV sterilizer can prevent the spreading of waterborne diseases in the water. This is ultimately the only way to protect your beloved fish.

Recommended UV Sterilizer

I’ve created a list of the best UV sterilizers on the market at the moment to help you choose the best for your aquatic needs.

1. HALF OFF PONDS and Water Gardens Shock Wave Stainless Steel 55-Watt in-Line Clarifier


Ensure crystal-clear water with the Half Off Ponds UV light sterilizer for your fish tank, pond, waterfall, pool, and more. The unit is made from high-quality stainless steel, perfect for bodies of water up to 12,000 gallons of water. 

The two inlet and two outlet valves, which allow for greater installation versatility, are oversized.

Enjoy an excellent reduction in algae presence in your pond, even in direct sunlight. The UV light sterilizes your water feature’s water as you watch. The glowing light indicator ensures you can monitor whether the light is on or if it’s time to replace the bulb. Replace the light after 9,000 hours of filtration use. 


  • The light meets the latest specifications with a 55-watt UV lamp that offers optimal sterilization at a flow rate of 2,500 – 4,000 GPH
  • Installation can be done in various positions to suit your water feature’s plumbing layout best
  • Clean your green pond in less than 48 hours with continuous use
  • The stainless steel tube houses a quartz cover for the light, and it offers a higher reflective capability of up to 33%, which assists in the cleaning process
  • A two-year warranty ensures you can buy this unit with peace of mind


  • Some users reported issues with the hose connectors

Why We Like It

The stainless steel body has a nice finish, and it assists the unit with cleaning and clarifying your water features. Water turns crystal clear within a few days, and you can rest assured of excellent sterilization power compared to other plastic housing sterilizers. 

2. Sun Submersible UV Sterilizer

Sun Submersible UV Sterilizer    

The submersible pump offers excellent filtration and sterilization power. It’s ideally suited to a 75-gallon tank and achieves a flow rate of 210 GPH for the most efficient sterilization use. 

The 9-watt light bulb is easily replaced, offering great water clarity with sustained use. Easy installation and all the required fittings are included. Install the unit vertically or horizontally in your tank or sump. 

The pre-filter sponge helps remove any floating particles, and it’s reasonably easy to clean out the sponge and inspect the light. On average, the lamp requires replacement once a year. 


  • Includes everything needed to install the unit 
  • The light has its own pump, which helps reduce hardware in your tank
  • The light truly clarifies tanks and ponds in as little as three days


  • The light doesn’t include a useful user manual

Why We Like It

The light and filter are excellent at clarifying water with minimal disturbance of fish and aquatic life. 

3. Coralife Turbo Twist 6X UV Sterilizer

Coralife Turbo Twist 6X UV Sterilizer    

For an excellent aquarium solution to clarify your tank water, the Coralife Turbo Twist is a perfect choice. The UV light unit can sterilize tanks up to 250 gallons, and it’s designed to be as inconspicuous as possible. Hang the unit off the side or back of your tank or install it in-line next to the tank. 

This UV light is suitable for freshwater or saltwater applications, and it comes with all the necessary equipment to attach it to your tank’s hoses. 

The UV light monitor light lets you check whether the light is working without having to get creative to try and see into the outlet hose — no more blanket over your head to try and check the UV light. 

With a twist design, water spirals through the chamber, ensuring maximum light exposure to better sterilize the water. The UV light reduces algae and other harmful bacteria in your tank water for better clarity. 


  • The twist flow design helps reduce the overall size of the light while still offering excellent surface exposure to UV light
  • Two lights are fitted inside the light chamber, and these can easily be replaced with 18-watt lights
  • Reduces water odor
  • It is convenient to install the unit on the side of the aquarium or next to your external canister filter


  • The mounting brackets aren’t the best

Why We Like It

The twist design is innovative, and it helps reduce any algae in your tank as it ensures a better exposure to the UV light. 

Also Read: The Best Fish For 100 Gallon Tank.

4. COOSPIDER Aquarium Filter Sun JUP-01

COOSPIDER Aquarium Filter Sun JUP-01    

Why not combine UV light sterilization with essential filtration? Using the Coospider filter gives you the best of both worlds. Use the unit to sterilize the water with the built-in UV light while the filter sponges remove any micro-particles that could make your water murky if left to float in the water. 

The unit has a compact design, and it’s fairly easy to open the housing to check on the light and the quartz housing around the light bulb. Fit the light in your tank submerged in the water to obtain maximum benefit and water clarity. The light doesn’t require an external pump, and with the air hose fitted, it also oxygenates the tank water to ensure healthy and active fish. 

The flow rate of 210 GPH is perfect for a tank of 40-80 gallons and ensures the light has optimal exposure time to the water as it cycles through the unit.  


  • Includes all the necessary accessories for installation 
  • Excellent water clarification and green tanks turn clear in a few days
  • A spare bulb is included, so you won’t have to purchase a new light for many months
  • The water outlet can be adjusted, which helps better filtrate your tank
  • Affordably priced


  • The pump may be too strong for tanks under 60 – 80 gallons or for tanks with delicate fish or crustaceans 

Why We Like It

We love the unit’s versatility with flow adjustment, filtration sponge, and even aeration. It’s a one-stop water clarifier for your aquarium. 

5. Aquatop 72-126 GPH Internal Filter with 7W UV Light

Aquatop 72-126 GPH Internal Filter with 7W UV Light    

The Aquatop UV light sterilizer is included in a filter-designed unit. The light is suitable for up to 70 gallons, and the 7-watt UV light ensures excellent water clarification. The pump produces a flow rate of up to 126 GPH, so ensure the flow rate isn’t too strong for your tank occupants before purchase. 

Use the UV light filter in freshwater or saltwater tanks. It comes with everything you need for installation in your tank below the waterline. Place the light in your aquarium, the sump, or your indoor pond. 

Installation is easy, and it works with most plumbing setups. 


  • Ideal for small to medium size tanks
  • Excellent water clarification is achieved in a few days of use
  • Energy efficient due to the 7 watts pump and 7 watts light
  • The UV light has an independent light switch 


  • The suction cups aren’t great, and the unit may slide away from the tank glass

Why We Like It

The light has separate light controls and power cables, which allow you to choose when you’d like to filter and when you’d like to add the UV light to your tank’s circulation system. 

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