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