Last update: November 3, 2022

Aquarium Air Check Valves – Save Your Tank!

It may surprise you to learn that your air pump could actually suck all the water out of your tank.

If your air pump is positioned below the level of the air tube or airstone in your aquarium, you are at risk.

Let’s say your pump stopped working or the airline tube became detached from the pump. This is when your friendly air pump turns into a water sucking monster.

The water pressure can cause a siphon action to occur – similar to how you perform a water change or use a gravel vac.

Once this starts, it’s not going to stop until every last drop of water has drained from your aquarium. And, that’s bad news for your fish!

Fortunately, this can be prevented…

All you need is a simple little device called an aquarium check valve.

And today, I am going to teach you all about it.

What is a check valve, and what does it do?

Aquarium check valve diagram

Sometimes referred to as non-return valves, a check valve is a small fitting that sits inline on your airline or any other aquarium tubing.

While it might not look like much, a check valve has a very important purpose:

To stop the water in your tank from flowing back out your airline.

Air or water can freely move through the valve in one direction. But if water comes down the tube, it will be unable to drain any farther than the check valve, which will stop the water in its tracks – never worry about backflow again!

The best thing about check valves? Once installed, they require no effort on your part. Simply place the check valve on your air pipe, and your aquarium is protected from the siphon effect, whether you are there or not.

While check valves are best known for their role in air pumps, they can also be used for CO2 lines and sumps. However, the general consensus among the community is that if you need to rely on a check valve for a sump, you should redesign your system – use a siphon break instead![1]

Do you need a check valve?

Inline check valve installed on aquarium airline tube

Well… No.

Your air pump is going to work just fine without it.

A check valve is only there as a failsafe – just in case something goes wrong.

Think of a check valve as a seat belt. 99.9% of the time it will sit there doing nothing. But if an accident occurs, you will be glad to have it.

Besides, given that a check valve is only going to cost a few dollars and could save you hundreds or even thousands of dollars in the event of a disaster, there is little reason not to install one on your air pump.

Alternatively, you can always place your air pump above your aquarium, such as on the hood. This also prevents the siphon effect from occurring since the airline is going up to the air pump instead of down.

But even so, I would still recommend installing a check valve just in case – accidents happen, and your air pump could get knocked to the ground!

Besides, installing a check valve takes just a minute…

Where do you place the check valve on your airline?

Stainless steel aquarium check valve

The best location to place the check valve entirely depends on the different fittings you already have installed on your airline tube.

1. Installing the check valve on a plain airline

If there is nothing else but an airline tube running from the pump to your aquarium, you can install the check valve wherever you see fit.

It may seem obvious, but this is an easy point to overlook:

Install the check valve in an easy-to-reach location.

There is no need to make life harder for yourself – you may need easy access to the check valve in the future, say to replace the tube or valve.

Your future self will thank you if you install it in an easily accessible location.

2. Installing a check valve on an airline with other fittings

Have a more complicated setup? Don’t worry – I’ve got your back!

Check the table below to learn where to place the check valve.

An opening in the pipe After
Bleed valve After
Airline control valve Before
Airline connector Before or after
3 or 4-way connectors Before or one on each tube after
Gang valve Before or one on each tube after

How do you install a check valve?

Installing an aquarium check valve on airline tubing

Simply choose a location on your air pipe where you want to insert a check valve.

Then, using a pair of sharp scissors, cut through the air pipe.

Now all that’s left to do is to insert both pieces of pipe into either end of the check valve, and you are good to go.

While the entire process is easy, there is one mistake many beginners make – installing the check valve with the wrong way up.

The check valve only allows the air to flow through in one direction.

If you installed the check valve upside down, no air is going to flow through the valve.

So if you find that your check valve isn’t working, simply remove the pipes and flip the check valve around – no harm done.

You can test the direction of the check valve by blowing into it with your mouth. You will only be able to blow into one end. Whatever end you can blow through, that’s the end that goes on the air pump side of your airline.

Once you finish, draw an arrow on the check valve to indicate the way the air flows. This way, if you ever need to remove the check valve in the future, you will know the correct direction when you put it back on.

Which is the best check valve for your aquarium?

Three different aquarium check valves in a row

Convinced you need a check valve on your air pump?

Good. Now all you need to do is buy one.

But with so many different check valves available, how do you choose the right one for your aquarium?

Well, let’s look at the boxes you need to check to find the best check valve:

Step 1: Make sure it fits!

First, you want to choose a check valve that fits your airline.

The standard-sized aquarium airline tubing is 3/16 inch (5mm). If you bought your airline from a pet store, then chances are this is the size you have. Aquarium check valves are specifically designed to fit this size tube.

That said, it is not uncommon to come across air pumps with different-sized tubing. That’s why you should always…

Measure your air tube!

To do that, measure across the inside of your airline. This is the internal diameter (ID). Use this measurement to find a check valve that will fit.

Check valves come in all different sizes to fit a variety of tubing, so even if your airline is an unusual size, you will have no issue finding a check valve.

If you are not confident, cut a small piece off your airline and take it with you when you go shopping for a check valve.

Step 2: Choose an appropriate check valve

Now that you have the correct size, it’s time to choose from the many different styles, shapes and brands of check valves available….

Who would have thought that a check valve would have so many options?

Well, I’m going to make it a little simpler for you. When it comes to check valves, I recommend United States Plastic Corp.

They sell the same check valves that you find in your local or online fish store for a fraction of the cost.

Seriously, I have seen the same check valves that can be picked up here for just a few dollars, but they sell for over $20 at specialized reef supply stores.

Why pay extra for the same thing?

Now, I must add that those cheap plastic check valves on Amazon are trash. Avoid them!

So, that’s why I am recommending United States Plastic Corp. Inexpensive but high-quality check valves.

Below are four common applications for aquarium check valves…

Airline check valve

3/16 inch 5mm ball and spring check valve for aquarium air tube

Cheap and effective – this check valve puts those check valves found on Amazon and eBay to shame.

I recommend buying a second one as a spare, just in case you need a replacement down the road. At this price, why wouldn’t you?

Ozone check valve

Ozone-safe Kynar check valve for aquarium

If you are injecting ozone into your aquarium, use a Kynar check valve.

High concentrations of ozone can melt a standard or nylon check valve in just a few days. Kynar is ozone-resistant and easy-to-shape, making it the ideal material in an aquarium check valve.

CO2 check valve

If you want an affordable CO2 check valve, either of the previous two options are more than appropriate.

Saltwater-safe check valve

The biggest problem with check valves is that they often rely on a steel ball or spring to operate.

If you have a saltwater tank, you know just how fast metal corrodes. And in the case of a check valve, it can actually rust in the open position. This means that the check valve is not protecting your tank.

While you could just buy cheap check valves and replace them every six months, this relies on you remembering to swap it out.

Fortunately, there is a check valve that promises to be more resistant to corrosion than stainless steel. And, although my experience with it is limited to just a few months, I am actually very impressed with the product.

Check it out here!

If you are looking for a high-quality check valve for your saltwater tank, this is worth investigating.


Who knew there was so much to learn about such a small valve that will, for the most part, go unnoticed in your aquarium?

As you see, with the exception of sumps, a check valve is essential if you are running any type of tube or hose into your aquarium setup.

I highly recommend spending the few dollars to drain-proof your tank. It might save you a lot of money and hassle in the future.

Do you use a check valve on your aquarium? Let me know in the comments below!

Ian Sterling

Ian Sterling, founder of, began his aquarium journey over 30 years ago, driven by a deep fascination for fish and their diverse personalities. His website,, is dedicated to making fishkeeping accessible and enjoyable, offering beginner-friendly guidance, expert insights, and a community for aquarists to connect and share experiences.

Comments (18)

I couldn’t tell which way to put the check valve on the tubing. I tried blowing into the check valve from both ends but couldn’t get air through. I cut the line and instead the check valve and the bubbler started working so I assumed I had it in correctly. I decided to make sure by taking it off and inserting it the other way thinking if the bubble came out one way they shouldn’t if I flip it around…problem is they did. The bubbles come out of the air stone no matter which way I turn the check valve… So how do I know if I’ve got it facing the correct way?? Thanks!

Hi Lori,

It’s not uncommon to have a faulty check valve, these are often sold in packs of five and are often cheap pieces of plastic. I often have 1 or 2 that don’t work. It should block air off from one side, so if yours doesn’t it’s faulty. If it doesn’t work, you’ll have to take it back and get another. I’m sorry to hear about your negative experience.

Thank you for the reply and confirming that it must be faulty and not just me. I will return it to the store and pick up another one. Thanks so much!

Not a problem Lori,

I hope you have better luck with the next check valve. Perhaps open it in store and blow in it then and there to confirm it’s working? This way you won’t have to go back to return it!

I have an outdoor fountain. I have (4) bubblers & (4) check valves installed on my fountain for a large bubble effect. I use a strong air pump. I can’t remember the name brand. I use (4) check valves to keep the water from flowing from my fountain to my air pump. The water from my fountain usually doesn’t flow to to my pump for a few weeks. This time the water leaked within a few hours of installing the same brand on check valves from the same pet store. I’ve used other check valves from other pet stores, but I like these particular ones. I thought my problem was the check valves unscrewing themselves & leaking from the seam, so I put aquarium silicon
around the check valves body @ the seam with & I’m still getting water to my pump. Please help what do you recommend. Thanks

Hi Patrick,

Unfortunately, this is a trial and error one. If the check valves are working, then water shouldn’t flow past that point. If they aren’t then you’ll have to swap over to something else. It doesn’t matter how much you like these particular ones, if they don’t work then they are not doing their job. If they are preventing water from flowing back then the water is coming from somewhere else. Because this is outside, it could be from anywhere. You’ll have to physically monitor and observe where it’s coming from. Does this happen after it rains? Is water traveling down the outside of the airline pipe? Is the ground the pump sits on getting wet somehow? Etc. These are all things you need to look for. Once you figure it out, you’ll know how to fix it.

I have just bought an Aqua One check valve for my air stone and pump. The pump is a replacement and I looked online just to make sure that the check valve will be facing the right way along the line. I can blow air one way and not the other way. OK, I knew that already. My probem is that NOWHERE on the internet is any description or picture of the check valve being put onto the air line, showing in which direction it is to face. My new check valve does not have an arrow, and there are no instructions or a diagram on the packet, even though the valve has two distinctly different ends. OK, I know which way it should face, because I already have one on another line. But why is the most simple and basic instruction not shown online? These accessory products are cheap these days, but so is human dignity, if something goes wrong and the only option is to throw the whole thing out and start again. Your blog has the most information, but in this instance only from a question someone asked. A faulty valve does not answer the question for a valve that has two distinctly different ends – which way is it supposed to point? I suspect that a frustrated customer will try to blow both ends and I also suspect that a little air will still escape into the airstone whichever way the valve is pointing, but that does not answer the most simple and basic question that has not been answered anywhere, even when pictures of the actual valve has been shown – which way is the valve supposed to face?

Hi A Ryan,

I understand your frustrations. I am not familiar with Aqua One, It doesn’t sound like an American brand. There are so many different check valve designs, shapes and sizes, that it would be almost impossible to list installation instructions for all of them. It should be the manufacturers responsibility to supply instructions for their product.

If you blow gently, air should only be able to move through the check valve in a single direction. If your check valve allows you to gently blow through both sides, then it’s faulty and should not be used. Because this is what all check valves have in common, it’s the easiest way to describe it. The side your lips touch when air blows through is the side you connect to your air pump.

I’m sorry I couldn’t help you more!

One thing not mentioned is that some check valves can also damage your air pump by increasing back pressure on the diaphragms in the pump itself. I run the tetra 100 whisper and went through 3 in a matter of 1 month due to check valves restricting airflow to some degree but even that is enough to damage some pumps.

Hi Vert_z,

I’m sorry to hear about your troubles, that must be frustrating. You are very correct. I cover backpressure more in my air pump review. It’s more common in airline control valves than check valves. It’s why I recommend using a Bleed valve to adjust the pressure.

Do check valves free up over time? I’ve just installed a aqua one valve, I’m getting bubbles from my stone but I pretty much have to pump as high as it goes.
I couldn’t blow air through either end, will the air flow improve?

Hi Dane,

It sounds like you have a faulty check valve. Unfortunately, this isn’t uncommon as many check valves are often poorly made. I’ll often buy a packet of 5 or 10 and have a couple fail. If you can’t blow through one side then it’s no good and you’ll have to discard it.

I have an outdoor fountain. I have (4) bubblers & (4) check valves installed on my fountain for a large bubble effect. I use a strong air pump. I can’t remember the name brand. I use (4) check valves to keep the water from flowing from my fountain to my air pump. The water from my fountain usually doesn’t flow to to my pump for a few weeks. This time the water leaked within a few hours of installing the same brand on check valves from the same pet store. I’ve used other check valves from other pet stores, but I like these particular ones. I thought my problem was the check valves unscrewing themselves & leaking from the seam, so I put aquarium silicon
around the check valves body @ the seam with & I’m still getting water to my pump. Please help what do you recommend. Thanks

Hi Patrick,

Pond air pumps are generally stronger than the type you would use in an indoor aquarium. It’s possible the check valves you are using are not rated for this amount air flow? I’d suggest calling the manufacturer of the air pump and see what they recommend you use with their product.

Great blog Ian! Lots of good information here. I see there are a number of material types listed on the USP page (e.g. Kynar, Polypropylene, Nylon) and seal types (Buna-N or Viton.) Do you have any thoughts on these and a recommendation?

Hi Jose,

For a basic aquarium setup, it shouldn’t make too much difference. I know many others who use those cheap dollar check valves from a local fish store. Assuming it works from the start, it will last for years. The oldest one of mine is going on 8 years old now, I think. If you have a very expensive setup, it could be worth investigating further.

I noticed my check valve had water in it so took it off n water started to fill up in my air line tube from biorb tank I’ve managed to put the air tube back into tank so it dosnt drain my tank and am getting a new check valve today but will the water that’s in the tube go back into tank when I replace check valve

Hi Madalaine,

The water in the airline tubing will need to be emptied back into the tank. If the new check valve works, then the airflow from your air pump should push it back.

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