The Fluval Hang-On Breeding Box Medium provides a safe, separate space connected to your aquarium where young, stressed, or new fish can be kept under stable water conditions. Because it hangs on the outside and uses water from your main tank, your fish benefit from the same temperature and water quality while remaining physically protected.

Designed with beginners in mind, this unit is simple to set up, easy to observe, and compact enough for use on small and medium aquariums. It is ideal for livebearers, shrimp, and delicate species where controlled breeding and careful acclimation are important.

Main features and benefits

• Multi-functional breeder and holding box for breeding, rearing fry, isolation, acclimation, and temporary holding.

• External hang-on design that saves internal tank space and makes observation and maintenance very convenient.

• Gentle, air-driven water circulation that continuously draws water from the aquarium into the box and returns it, helping maintain stable parameters for sensitive fish.

• Ideal as a hatchery and incubator to reduce fry losses by separating them from adult fish that may prey on them.

• Provides a safe haven for injured, weak, or bullied fish, allowing stress-free recovery without leaving the main system.

• Useful for acclimating new fish as they experience your tank water while remaining physically separated from established inhabitants.

• Clear plastic construction with a tight-fitting lid allows easy viewing and reduces jump-outs.

Technical specifications

How it works:

The breeding box hangs on the outside of your aquarium, and an air pump pushes air through the included airline tube to pull water from the main tank into the box. Water then gently flows through the box, keeping oxygen levels and temperature similar to your aquarium before returning back to the tank.

For breeding, the included V-shaped separator or grid can be used to let eggs or fry fall safely away from adult fish, greatly improving survival. For isolation or acclimation, you simply place the fish into the box and let them settle in while still enjoying the benefits of your established aquarium water.

Installation tips for beginners

• Ensure your aquarium glass or frame thickness matches the recommended range before installation.

• Hang the empty box on the aquarium and use the leveling adjusters so the bottom of the box is straight and secure.

• Connect the airline to your air pump, adjust the included valve to achieve a smooth, gentle flow, and confirm continuous water movement through the box.

• Always use a lid to reduce the risk of fish jumping out and to maintain a calm, protected environment for fry.