Check Valves For Aquariums

Aquarium Check Valve

Fish tank with air tube

Figure 1: Fish tank with air tube

Aquarium check valves are a vital component to a properly functioning fish tank to keep your fish alive and healthy. These valves are necessary when operating air pumps. Air pumps feed air to various aquarium devices - such as filters, bubblers, air stones, and decorations - to keep oxygen levels in tanks high enough for fish to survive. If something interrupts the pump’s operation, for example, a power outage, there could be significant issues.

When the air pump shuts off, the air in the tubing flows back to the pump, creating a siphon and bringing water with it. If the water is moving fast enough, it can flow over the rim of the tank. Without an air pump check valve, siphoned water will not only damage the air pump but will likely flood the area around the tank and damage any other electronic equipment it contacts. Eventually, if left unchecked, the tank will empty.

How an aquarium check valve works

An aquarium check valve, also known as a non-return valve or a stopper valve, will allow air to flow from the pump to the connected device(s) but will not allow air, and more importantly, water, to flow back towards the pump. A typical check valve design for an aquarium uses a conical rubber valve housed in a plastic casing. The tapered end of the valve points toward air flow and opens when air is flowing, then automatically closes when airflow stops. When it’s closed, water cannot pass through the valve.

Selecting an aquarium check valve

Material and size are two important factors when choosing a check valve for an aquarium.

  • Material: While most aquarium check valves are plastic and rubber, stainless steel and bronze check valves are available too.
    • Metal: Metal check valves are unsuitable in saltwater aquariums because they corrode over time.
    • Kynar: Kynar check valves are specifically for when ozone is pumped into an aquarium. Ozone can melt other plastics.
  • Size: The check valve needs to fit with the air tubing’s diameter. If it is necessary to measure the diameter of the tubing, measure the inside diameter of the tube. Standard tubing is 3/16 inch (5mm).

Installing an aquarium check valve

In most cases, installing an aquarium check valve is a straightforward procedure. First, determine where to install the valve. As demonstrated in figure 2, the recommended location is near the tank’s rim. Installing the check valve near the pump will allow water pressure to build further before encountering the check valve, which may lead to leaking.

Simple aquarium air pump (B) and check valve (A) setup. The device in the water (C) could be a sponge filter or air stone.

Figure 2: Simple aquarium check valve (A) and air pump (B) setup. The device in the water (C) could be a sponge filter or air stone.

After determining where to install the check valve, use a sharp pair of scissors to cut the air tube at that spot and then attach each piece of air tubing to each end of the check valve. The valve’s connection points are slightly tapered at the tips where the tube slides on, and broaden closer to the valve body. This gives a tight seal between the tubing and connection points. The only common error made during this process is installing the check valve in the wrong direction. Ensure that the arrow on the valve points towards the direction of airflow.

The above installation instructions assume that the check valve is the only fitting installed on the tubing. Where to install the valve is a little more complicated when other fittings are present. An aquarium check valve should be installed:

  • After an opening in the tubing
  • Before an airline control valve
  • Before a gang valve
  • After a bleed valve
  • After or before an airline connector

Is an aquarium check valve necessary?

There are pros and cons to adding a check valve to an aquarium air pump setup:

  • Pro: Extra protection in case the air pump stops working.
  • Cons: The check valve might leak and will restrict airflow. If the tank is sized precisely for the air pump, adding a check valve will result in less air than necessary in the tank.
  • Solutions: Having peace of mind is worth trying to solve the downsides of check valves. To prevent leakage, ensure that the valve fits properly and use hose clamps for a tighter connection. Regarding airflow, choose a pump that is oversized for the tank and a check valve with a low cracking pressure.

There is disagreement on whether or not aquarium check valves are necessary. Those in favor promote check valves for peace of mind. Those against check valves argue that they will eventually leak and are undependable. The alternative to aquarium check valves is always ensuring that the air pump is installed above the tank’s waterline. If water does get siphoned through the air tubing, it won’t be able to back up higher than the height of the tank.


What does an aquarium check valve do?

An aquarium check valve lets air flow from the air pump and into the tank but does not let air or water flow back towards the air pump.

Do you need a check valve for an aquarium?

A check valve is unnecessary for an aquarium if the air pump is placed above the aquarium’s waterline. In the case of water siphoning, the water won’t be able to flow much higher than the height of the tank.

Where should I put my aquarium check valve?

A check valve for an aquarium should be near the rim of the tank rather than near the air pump. This will stop the siphoned water near the source and help prevent valve leakage, which may happen if the valve is installed further down the line.