Fish Tank Siphon Stopper® Aquarium Output Nozzle

Fish Tank Siphon Stopper® Key Features

  • Patent Pending air intake cap automatically breaks a back siphon should the water flow stop
  • Minimizes flood risk and volume of back siphon during a power outage or pump failure
  • Works great with the Seamless Sump® system!
  • Does not rely on check valves with failure prone gaskets or springs
  • Loc-Line knuckle allows many output positions and nozzle options
  • Siphon Stopper® cap allows surface circulation and aeration
  • Siphon stopping cap is above the waterline, yet below the lids to minimize evaporation
  • Can be manipulated in multiple positions to easily control water circulation
  • Easy installation, all that is needed is one hole drilled for a 1/2″ bulkhead
  • Order the aquarium from us and we can drill holes for your overflow and returns for you!
  • Hole drilling kits available for easy DIY installation on existing aquariums
  • Fixed drilled position reduces the probability of human error
  • Installs out of your line of sight, very little visual impact on the look of your aquascape
  • Clean, professional look – no “sloppy tank” syndrome

Fish Tank Siphons Stopper® Aquarium Systems

The patent-pending fish tank Siphons Stopper® is a great way to minimize the risk of a back siphon into your sump and at the same time gives you great flexibility to manipulate the water flow of your tank without introducing excessive evaporation. No more reliance on failure-prone check valves!

Typical Water Line with Pumps Off

Output fitting goes above the water line then back underwater to prevent excessive evaporation. This, plus allowing air to enter at the cap above the waterline will prevent a back siphon when a pump stops.

Output Nozzle Placement

With the Siphon Stopper® aquarium systems in place, you can put the output nozzle at any height in the tank you want to increase circulation without risking a back siphon past the overflow height.

Fish Tank Siphons Stopper® Cap

Above the waterline yet below the lids- lets a small stream of water out while pumps are running. Lets air in immediately to break the siphon should the pump stop running for whatever reason.

Aquarium Siphons Stopper® Vs Failure Prone Check Valves

  • Check valves require a perfect seal to work…
  • Siphon Stopper® does NOT require a perfect seal to work!

Importance of Preventing a Back Siphon

In the event of a loss of power to your water pumps for a variety of reasons, if your return output nozzle is below the waterline of the aquarium it can create a back siphon and can discharge water from your aquarium into your sump at a very quick rate. The lower your output nozzle is in your aquarium, the more water will discharge into your sump. The water will continue to back siphon into your sump until the water line in your aquarium is below the return nozzle or the introduction of enough air into the line has the chance to break the siphon (notice: air must be introduced at a specific point in the line in order to effectively and reliably break the siphon). If your sump does not have the volume capacity to take on all of this additional water this can create a flood which can be an emergency situation both for the safety of your fish and you and your personal property. Read our Risk of Flood Disclaimer to find out more.

Causes of a Back Siphon

Usually, a back siphon would occur in the event of a power failure, equipment failure (pump failure), or if someone does not pay attention to water levels in the sump when servicing the aquarium. Even if you have a sump designed to have enough volume to take on all the excess water in the event of a back siphon, if the person filling your tank does not pay attention to acceptable water levels and overfills the sump in the first place, a flood can happen.

For these reasons, it is important to have measures in place to stop a back siphon as reliably and quickly as possible in the event of a pump losing power and a stop in water flow. The patent-pending Siphon Stopper® is the best and most reliable solution.

Inherent Fatal Flaws of Check Valves

As mentioned above, the fatal flaw of practically every check valve design is that they require a perfect seal of a mechanical contraption in order to work properly. Most check valves are either created with a “floating ball valve” design or a “spring valve” design. With the floating ball valve design, there is a ball floats within a valve when the water is high creating an opening to let water through, and sinks and mates with a rubber gasket to create when the water goes the opposite, or undesired direction. With the spring valve design, there is a membrane or a flapper that uses a low tension spring to hold the gasket shut. The water pressure flowing in the correct direction will push the spring gasket open, when going the wrong direction or neutral the gasket closes, yet still relies on a perfect seal to work. Both of these designs also starve a little bit of energy from your water pressure by restricting the flow rate.

For either design when a return line backflows if there is even a small gap or imperfection in this seal the check valve will leak. This leak could either slowly or quite quickly cause a flood in your sump which could result in severe property damage, possibly even fire, electrocution, and serious injury or death if water gets into your exposed electrical components. Read our Risk of Flood Disclaimer to find out more.

There are many reasons, a seal in a check valve could leak. Since aquarium environments are often caustic saltwater or hard water environments, sometimes intentionally with a variety of minerals and particles and organisms present, it just does not seem wise to rely on a mechanical contraption that is constantly being submerged and subjected to factors that could lead it to fail. Degradation of the seal materials, build-up of minerals, corrosion of the springs, etc… are just a few ways that the valves could become ineffective over time. Just think about it- you are relying on a complicated mechanical contraption that has been submerged in water, sometimes for years, which is rarely if ever tested. They are relied upon usually in an emergency situation with a power outage or equipment failure. Often times in the event of a power outage since there is no power your options are limited to try to stop the flood. And let’s face it, when a power outage happens you likely have more things to worry about than whether or not your check valve is going to hold up… it is probably the last thing on your mind and there may not be anyone near the aquarium at the time to check on it. The most likely way to find out your valve is going to fail is by wading through a pool of water on your floor. Relying on a failure-prone check valve just seems like a situation destined for a bad ending.

No longer is there a need to rely on failure-prone check valves… through our experience- we created the most reliable Siphon Stopper® solution!

Fish Tank Siphons Stopper® – No Perfect Seal Required!

The biggest advantage of the Siphon Stopper® design is the fact that there is no seal required to break the siphon. The very same flaw of the check valve design is the advantage of the Siphon Stopper® aquarium systems. When the water flow is shut off or reverses course, air will automatically enter the cap that is positioned in just the right spot above the water line and break the siphon. The only thing that is required for this to work is for the air passage to remain clear of debris. It doesn’t even need to be “perfectly” clear, just clear enough to allow enough air in for the siphon to break. Being that it is above the water line and has a small stream of water coming out of it at all times, this should be easy to accomplish and easy to monitor. This will work no matter what height you have the output nozzle in your tank so long as the Siphon Stopper® cap remains above the water line. This, and the Loc-Line knuckle on the end of the output fitting, gives you even more flexibility to add longer output lines to manipulate the circulation of your aquarium.

Multiple Positions to Manipulate Water Flow

The Siphon Stopper® cap, elbows, and the Loc-Line output nozzle can be easily manipulated in multiple directions in order to control your water flow and circulation. This also helps keep it out of the way of your lighting and other aquascaping features.

Cap and Elbows Easily Twist

Versatile way to manipulate water flow and stay clear of aquascaping

Loc-Line Knuckle, Hose, and Nozzle

Easy to extend length, bends in any direction, and attaches easily to a variety of nozzle shapes and sizes

Loc-Line Attachments Available

Our Siphon Stopper® return fitting is Loc-Line compatible which makes it very convenient to expand and modify your hose and nozzle. Loc-Line has a full range of attachments available to meet many needs. We stock some of them and sell them on our website on our Loc-Line attachment ordering page, others are available online at

Attached to Aquarium in Fixed Position for Safety

Because of the importance of keeping the air intake of the siphon stoppers’ caps above the waterline and below the lids, we take no chances with the height positioning. A permanent hole drilled in the glass makes sure the Siphon Stopper® is always secured at the proper height. Order the aquarium from us and we can drill it for you for a small fee. Or, order a hole drilling kit for easy installation on existing aquariums.

No “Sloppy Tank” Syndrome

Another advantage to having the return outputs attached in a drilled, fixed position is you can maintain a consistent, professional appearance. Being that these parts are all designed by our service experts at Serenity USA, consistently maintaining a professional appearance is very important to us.

One of the things you will find in most aquarium setups is the fact that the output fittings tend to have an unprofessional appearance. They are usually hanging off of the back of the tank in sort of a crooked, sloppy-looking position. Most fittings are either suspended freely or held in place by suction cups that rarely maintain their grip over time. Even if the person servicing the tank is diligent about putting them in a good position each time, the water flow, algae cleaning scrapers, and fish movement tend to quickly jar them out of place. You get an inconsistent look and an inconsistent position of your output nozzles that will affect the water flow and just plain look bad.

This simply won’t happen with Siphon Stopper® aquarium systems. Your outputs will remain in a fixed position indefinitely giving your aquarium a professional appearance year after year and at the same time a consistent and easy way to manipulate water circulation.