5 Best Hang-On Overflow Boxes

If you’re experienced with owning an aquarium fish tank, you’ll be well aware of the dangers that come when a tank overflows. While this may not seem like a common problem, if your air pump becomes faulty while you’re at work or your filter becomes blocked while you’re in the other room with your headphones on, the water damage can cause so many issues.

Imagine all the plugs, electrics and cables you have laying around and now imagine gallons of water going all over them. In most cases, it’s simply not worth the risk. This is where hang-on overflow boxes. As the title suggests, this is a mechanism that you can hang onto the side of your tank to capture any water that could potentially overflow and cause issues.

What’s more, most of these boxes have the capabilities to pump water back into your fish tank which is a really nifty feature if you’re experiencing water loss due to evaporation. All in all, these are serious pieces of equipment that any fish tank owner should think about investing in.

However, the question remains; which hang-on overflow box is best for you?

Fortunately, we’ve searched far and wide looking for the best devices in this category to find which will be the most helpful. Below, we’re going to explore the ins and outs of our favorite five that we know you’re going to love, detailing everything you need to know to make the right purchasing decision.

Let’s go.

CPR Aquatic CS102 Deluxe Siphon Overflow

CPR Aquatic CS102 Deluxe Siphon Overflow

To start off our list, we’ve chosen the CPR Aquatic overflow box. This is a powerful overflow box that comes with all the features you’d be looking for in a device like this and more. This device comes at a mid-range price making it suited for all buyers, no matter what budget you’re on.

What you’ll love about this siphon is the fact it’s not only an overflow box for water to flow into, but it will also filter any water that enters it. This means all the water that goes back into your tank is filtered to maintain water quality and prevents any risk of contamination.

Another cracking feature of this device is the fact that it has a siphon design. This means the device is basically pipe-less, allowing it to capture and hold up to six times more water than conventional overblow boxes.
Installation is simple as you can easily hook the unit over the edge of your tank securely and there it will stay.

Looking through reviews of this device, there’s practically nothing bad to say about it. All the past customer reports we could find where outstanding and reported no negative points, making this easily one of the best overflow boxes available today!

  • A pipe-less design to hold six times more water than conventional overflow boxes
  • Filters water automatically to prevent contamination
  • Suitable for buyers on any budget
  • Easily installs onto the side of your aquarium
  • None!

CS100DX Deluxe Model Overflow Box

CS100DX Deluxe Model Overflow Box

Another mid-range overflow box, the CS100DX is a handy and affordable overflow box that makes it easy to minimize the risk of overflow. In fact, this is such a powerful, large capacity device that it can handle, and filter, up to 800 gallons per hour; a huge volume of water compared to other devices.

What you’ll love about this device is the fact it comes with a lid to help trap water to stop splashes or accidental overflow and an aqua lifter that can help pump any lost water back into your tank or to replace lost water from evaporation.

Just like the overflow box above, this box is designed with capacity in mind and uses a very minimal number of tubes. This means the device can hold up to six times more water than a conventional overflow box and can process the water much quicker.

After extensive searching, we found this to be another extremely high rated overflow system with nearly a dozen highly acclaimed reviews that state the box is easy to use and does exactly what it’s supposed too.
The box takes less than 30 seconds to set up with an easy installation process and once activated, it operates quietly, so it’s sure not to distract or annoy you. All in all, this a great overflow box where you can’t go wrong!

  • It takes less than 30 seconds to set up and install
  • Can hold up to six times more water than conventional boxes
  • Can actively replace lost water in your tank from overflow or evaporation
  • Can process up to 800 gallons of water per hour
  • None!

Aquaeon AAG29251 Overflow Accessory New Kit

Aquaeon AAG29251 Overflow Accessory New Kit

Aquaeon is renowned in the aquarium fish tank world for being reliable, trustworthy and creating high-performance products that are built to last and this overflow accessory kit is no exception to this rule.

Firstly, this is a really affordable overflow accessory designed to work primarily with glass tanks and fits nicely into the corner of the tank with next to no effort, and you’ll be set up and ready to go. However, what makes this kit unique is the fact it absorbs the water using a sponge system.

If the water overflows, then it’s soon sucked up by the sponges which you can empty manually back into the tank or allow the device to drip feed the water back into the tank. This also acts a filter for the water, and while it may not be as effective as the other devices, this is a true budget-friendly option.

This is an efficient system that’s suitable for tanks of any size and is regarded by many as a ‘must have for any kind of aquarium fish tank setup. All areas of the device are adjustable so you can fit it perfectly to your tank and you won’t have to worry about fiddling around trying to get things to work.

Everything is so simple. If you’re looking for an affordable, no-hassle device that’s inexpensive and does exactly what you want it to do, you won’t have to look further than this.

  • Really easy to set up and start using
  • Can be used on tanks of any size
  • An incredibly affordable price tag
  • Pumps and drips the water back into your tank
  • Doesn’t process water as fast as other boxes on our list

Eshopps AEO11005 Overflow Boxes PF-800 for Aquarium Tanks

Eshopps AEO11005 Overflow Boxes PF-800 for Aquarium Tanks

If you like the idea of having an affordable, pipe-based overflow system, Eshopps is another fantastic and highly rated option you won’t want to miss. This is simple to install onto your tank by hanging it over the edge where it’ll be able to capture any water that overflows over the edges.

This is then absorbed and filtered using the integrated cylinder foam inside the overflow box itself before being pumped back into the tank where it belongs. There’s no need to worry about silly overflows or the water level getting too low. This device has you covered.

Another really special feature of this device is the fact it’s a dual-piped design. This means that even in the event of the overflow pipe being blocked, there’s always another one for it to use, minimizing the overall overflow risk dramatically.

Once again, there’s really nothing negative to point out about this device, and it seems all the creases have been ironed out by Eshopps. If you do have any problems with any aspect of the device, make sure you’re reading the instructions thoroughly because this is a detailed guide with everything you need to know.

Suitable for all tank sizes and capable of pumping water back into your tank without causing bubbles, this is another high-performance, constant flow overflow box you’re going to love.

  • Suitable for fish tanks of any size
  • Pumps the water back into your fish tank
  • Dual-piped to prevent overflow in the case of a blockage
  • Comes with a full instruction guide to help you with any troubleshooting problems
  • None!

CPR CS90 Overflow Box

CPR CS90 Overflow Box

The final overflow box we’re looking at today has us heading back over to the CPR brand for another amazing device you’re sure to love and find a ton of value in. This is a low to mid-range box which means it’s moderately priced and suitable for all budgets while maintaining the quality and performance of a high-end overflow box.

Heading into the facts, this overflow box is capable of processing up to 600 gallons of water per hour and is suitable for aquarium fish tanks up to 125 gallons in size. It’s worth noting that the pipes on this device are a bit smaller than the other boxes on this list, it’s still fully capable of pumping the water back into your tank where it needs to be.

One of the great features we love about this overflow box is the fact you can set the water level of the overflow box to maintain a certain level. This is ideal if you want to automate the entire process, and great for if you want to lower the level for cleaning or maintenance purposes.

In short, this is another great overflow box to set up, and you’ll find no problems with it. If you do get stuck, you’ll find a complete instruction guide included that has all the information you’re ever going to need to know. Another great product from CPR!

  • Easy to set up and install
  • Comes with all the instructions you’ll need for troubleshooting
  • Built-in water level management tool
  • Can process up to 600 gallons per hour
  • Only suitable for fish tanks up to 125 gallons
  • Can process a limited number of gallons per hour compared with higher end boxes


As you can see, there are plenty of overflow boxes out there designed to make your life easy and can help take away the stress you may have when it comes to an overflowing fish tank. There’s no denying there are some great boxes out there that will get the job done, now all you have to do is find the one that’s right for you!

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