Where To Put UV Light In The Aquarium

Having an aquarium is a cool and enjoyable hobby. The colorful fish and the calm underwater world make a lot of people happy. But to keep your aquarium in good shape, you have to take care of the water inside it. 

One way to do that is by using something called a UV light sterilizer. These devices use special light to make the water clear and to get rid of tiny, harmful creatures in your aquarium. 

In this article, we’re going to talk about where to put UV light in the aquarium so they work really well.

But, before we get into that, it’s important to know how long you should leave these UV lights on. So, let’s get started with that first.

What Is The Recommended Duration For Leaving UV Lights On In The Aquarium?

UV lights are sometimes used in aquariums to keep the water clean by getting rid of tiny, harmful creatures that can make fish and other water animals sick.

Now, the question is: How long should you keep these UV lights on in your aquarium? Well, it’s suggested that you run these lights for about 10 to 12 hours each day. 

This amount of time is good because it helps to kill those harmful creatures effectively. Plus, it also gives the fish and other aquatic creatures in your aquarium a sense of a natural day and night cycle, which is important for their well-being. 

So, it’s like giving them a regular day with light and a regular night with darkness. This helps them stay healthy and happy in their watery home.

What Types Of UV Sterilizers Are Available?

UV sterilizers are devices that help keep your aquarium water clean by using a special kind of light to kill harmful microorganisms. 

There are different types of UV sterilizers to choose from, and the best one for you depends on how big your aquarium is, how it’s set up, and what you need.

1. Submersible UV Sterilizers

These are UV sterilizers that you can put right into your aquarium water. They’re good for smaller tanks because they can fit easily and work well in that size. They’re like a little underwater light that zaps the bad stuff in the water.

2. In-line UV Sterilizers

These UV sterilizers are designed to work with larger aquarium setups. They are connected to the external filters you might have on a big tank. 

Instead of going inside the tank, they’re set up outside, and the water flows through them to get cleaned up before it goes back into the aquarium. These are more suitable for big aquariums with lots of water to clean.

So, think about the size of your aquarium and how it’s set up when choosing between these two types of UV sterilizers. 

The goal is to pick the one that fits your aquarium’s needs best to keep the water as clean as possible for your fish and other aquatic buddies.

What Factors Should Be Considered When Selecting A UV Sterilizer And Pump For An Aquarium?

aquarium UV-light
Image Credit: petsradar.com

1. Aquarium Size

Start by looking at how big your aquarium is. If it’s a large one, you’ll need a UV sterilizer that’s powerful enough to clean all the water effectively. 

Just like you’d need a big vacuum cleaner for a large, messy room, a bigger aquarium needs a more powerful UV sterilizer.

2. Flow Rate

This is about how fast the water moves through your aquarium and the UV sterilizer. It’s important that the UV sterilizer can handle the amount of water your aquarium filter pumps through it. 

Think of it like a drinking straw – if the straw is too narrow, it’s hard to sip your drink. But if it’s the right size, drinking is easy. 

Similarly, the flow rate of the UV sterilizer should match how much water your aquarium’s filter pushes through it. This way, it can do its job efficiently, like sipping up the water to clean it.

3. Type of Organisms

Consider what problems you want to solve in your aquarium. Do you have too much algae growing in the water? 

Do you have issues with too much algae growing in the water? Are you worried about diseases that could harm your fish? 

Or maybe you just want to make the water look crystal clear. Different UV sterilizers are better at dealing with different issues. It’s a bit like choosing the right tool for a job. 

So, figure out your main concern, whether it’s algae control, preventing diseases, or just making the water nice and clear.

4. Installation

Decide where you want to put the UV sterilizer in your aquarium. This matters because it affects what kind of UV sterilizer and pump you’ll need. 

If you want to place it inside the tank, you’ll need a submersible one. But if you’d rather have it outside the tank, like connected to your filter, you’ll need an in-line unit. 

It’s a bit like deciding where to put a lamp in your room – on the table or on the ceiling. The placement affects how it works. So, think about where you want to install the UV sterilizer when making your choice.

Where To Put UV Light In The Aquarium?

When it comes to where to place UV lights in your aquarium, where you put them really matters because it affects how well they work. Here are some common places to think about:

1. The Filter System’s Inlet

One good spot to put UV lights is at the entrance of your aquarium’s filter system. This means that when water is sucked into the filter, it has to pass through the UV light first. 

The UV light acts as a guard, checking the water for any bad stuff before it goes into the filter and then back into your aquarium. 

This way, the UV light can clean the water right from the start, making it a smart place to put it for effective cleaning.

2. The Filter System Outlet

Another good spot for UV lights is at the end of your aquarium’s filter system, right where the cleaned water comes out before going back into the tank. 

Here, the UV light can make sure that only the water that has been properly filtered and cleaned gets exposed to it.

It’s like giving the water one final scrub before it goes back into the aquarium, which helps keep your tank water even cleaner. So, putting the UV sterilizer at the filter’s outlet is another smart choice.

3. Submersed In The Aquarium

Some UV sterilizers are designed to be placed right inside your aquarium, like an underwater light. These are called submersible UV sterilizers. They work well for smaller tanks.

When you put a submersible UV sterilizer in your aquarium, it can directly target and deal with issues like too much algae and harmful pathogens that might be in the water. It’s a bit like having a mini-cleaning device right inside your fish tank.

So, if you have a smaller aquarium and you’re dealing with problems like too much green stuff (algae) or you’re worried about diseases, a submersible UV sterilizer could be a good choice to keep things under control.

4. In The Sump

If your aquarium has a sump, it’s another good spot to place the UV sterilizer. A sump is like a hidden chamber or compartment that’s connected to your main aquarium.

You install the UV sterilizer inside this sump chamber. When the water from your main tank is pumped into the sump, it passes through the UV sterilizer before it goes back into the main tank.

It’s like a water-cleaning station tucked away behind the scenes. This way, the UV sterilizer can treat the water, getting rid of any bad stuff, before it returns to your main tank. 

It’s like having a secret water purifier that does its job out of sight, making sure your aquarium water stays clean and healthy. So, if your aquarium has a sump, this is a smart place to set up your UV sterilizer.

5. In Line With The External Canister Filter

If you have an external canister filter for your aquarium, you can use an in-line UV sterilizer with it.

You attach the in-line UV sterilizer to the plumbing of your external canister filter. This means that as water circulates through the filter, it also goes through the UV sterilizer.

Your canister filter is already working hard to clean the water, and with the UV sterilizer in line, it adds an extra layer of cleaning power. 

It’s like a double-check system, making sure the water is as clean as possible before it goes back into your aquarium.

So, if you have an external canister filter, using an in-line UV sterilizer is a smart way to make sure your aquarium water is super clean and free from harmful stuff.

6. Attached To The Surface

There are certain UV sterilizers that can be mounted right on the surface of your aquarium. This means they sit on top of your aquarium, usually near the water’s edge.

These UV sterilizers are designed to be discreet, so they don’t take up much space or draw attention. They’re like a small, quiet helper that works from above.

When they’re positioned like this, they shine their UV light into the water, and it helps clean up the harmful stuff. 

It’s sort of like having a guardian watching over your aquarium, keeping it clean without getting in the way.

What Are Some Disadvantages Of UV Light Sterilizers In Aquariums?

While UV sterilizers offer numerous benefits, they also come with a few drawbacks to consider:

1. Not Effective Against All Pathogens

UV light sterilizers are powerful, but they have limitations. They may not be able to get rid of certain types of harmful microorganisms, like parasites that are protected by tough shells (cysts) or tiny creatures hiding in hard-to-reach spots. 

So, while they’re great for many things, they might not solve all your aquarium problems.

2. Harmful To Beneficial Microorganisms

UV light doesn’t discriminate between good and bad microorganisms. It can also harm the helpful bacteria and microorganisms that play a role in maintaining a healthy aquarium ecosystem. 

So, while it kills off the bad stuff, it can also affect the balance of beneficial organisms in your tank.

3. Regular Lamp Replacement

UV lamps in sterilizers have a lifespan. They need to be replaced every so often to keep working effectively. 

This means you’ll have ongoing costs and maintenance to deal with, which can add up over time.

4. Cost

UV sterilizers, along with the cost of replacement lamps and electricity to run them, can be relatively expensive. So, while they offer benefits, you’ll need to consider the init


To sum it up, where you put UV lights in your aquarium is really important. It can make a big difference in how healthy and clear your water stays. 

So, when you’re picking a UV sterilizer, think about how big your tank is, how it’s set up, and what you need to fix. Then, choose the right spot to put the UV light that matches what you want to achieve. 

By doing this, you’ll keep your aquatic world lively and healthy while reducing the chances of common water problems.


Can aquarium fish see UV light?

Yes, some aquarium fish can see UV light to some extent. While humans can’t see it, some fish have special eyes that can detect UV light.

However, not all aquarium fish can see UV light, and it varies from species to species. UV light might play a role in their behaviors and communication.

Do aquarium plants like UV light?

Aquarium plants, like many other plants, don’t really use UV light for photosynthesis (the process that helps them grow). In fact, too much UV light can harm them.

So, for the health of your aquarium plants, it’s best to provide them with the right amount of visible light and not expose them to too much UV light.

Does UV light prevent algae?

Yes, UV light can help prevent the growth of algae in aquariums. UV sterilizers use UV light to kill tiny organisms, including the ones that can cause algae blooms.

By using a UV sterilizer correctly, you can reduce the chances of algae taking over your aquarium, which is good for the overall health and appearance of your tank.

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