Best Hang-on Overflow Boxes Reviewed

4 Top Ranked Super Sleek Hang-on Overflow Boxes

Most of the reef tank and aquarium lovers completely understand the importance of an overflow box. The prime advantage of utilizing an overflow box is that it makes sure that your display tank consistently maintains the optimal level of water all time.

To replenish evaporated water in an effective manner, overflow tank properly pumps in the optimal level of water quickly after sensing the low level of water in a tank. 

To remove the impurities, it also pumps aquarium water through a filter. Want to learn about the best auto feeders ?

Categories of Overflow Boxes

Overflow boxes are available in two distinctive types which are internal and external.

In most of the cases, the internal version is considered as the best option. It is very easy to customize and the best part is that it is very economical as compared to the external version.

It can be easily placed inside the tank and you can also cover it with a cabinet. But for doing all these things, your main aquarium tanks should have a drilled hole.

On the other hand, the external version would be a better choice if your aquarium does not come with predrilled holes.

Though, you can also drill holes on your own but it’s quite a troublesome task for anyone to do it with utmost perfection.

In addition, if there is not much extra space below your reef tank then also external version would work better.

It basically acts as a HOB (hang on back) unit. You can easily hang it at the back and to hide it, use your tank decors such as coral.

Moreover, there is no requirement of a drill as well because they can easily suck the water over the side of tank with the use of siphon.

The only disadvantage of this is that sometimes the air enters the siphon and thus water stops draining to the tank. This will eventually lead to the overflow of water as the pump continues to through back water in the aquarium.

Thus it is highly important to check that whether the overflow can draw out air or not.Thus, it is very easy to keep track of the quantity of water which is inside because an overflow box gives a clear view.

Purchasing a Hang-On Overflow Box

You can accurately decide which HOB overflow box will work great for your aquarium by using many different ways. In most of the cases, the manufacturer gives complete information about the selection of right aquarium size according to overflow box.

Another most important thing that you must consider is the right level of the overflow box flow rate. It should be rated quite higher than the return pump flow rate.This means you can utilize a 600gph if you own a 500gph return pump. 

The simple method to make the right selection is to check the exact size of your tank and multiply it by 10. It means if you have a 90-gallon tank then 900gph is optimal.In other words, it is perfectly fine to use a bigger overflow tank that offers a high flow rate.

This is because the overflow can accurately regulate itself and it will also restrict the pumping of excess water than the amount that needs to flow into it.

However, buying a larger overflow box will be quite costly for you as you are paying for greater capacity.

Other main factors that you should consider are:

  • Is it quick and easy to install?
  • Is there any chance of quick clogging?
  • How is the overall quality?
  • How much noise does it create?

The main thing is that it is all up to your understanding and choice to get the wet/dry filters, sump, refugium that you want for your tank.

Best 4 Super Sleek Hang-on Overflow Boxes

1. Eshopps Overflow Box

Eshopps AEO11005 Overflow Boxes Pf-800 for Aquarium Tanks
  • Each box includes everything required to install on your aquarium and includes; Foam prefilter, Clear U-tube syphon, nylon screw & wing nuts, black pre-filter box & 1 in. bulkhead drain.
  • The Eshopps PF-800 Hang on overflow box features a compact U-Tube Design
  • The PF-800 is designed for aquariums up to 125 gallons, and has a maximum flow rate of 800gph
  • At only 3" wide, minimal space is required between your tank and wall, these boxes are excellent for optimizing space.
  • The interior black acrylic overflow box is adjustable so you can set the water level in the aquarium where you want it, and efficiently pulls water of the surface to keep the surface clean

Last update on 2021-12-13 / Affiliate links / Images from Amazon Product Advertising API


  • It usually works in the proper manner as it claims, according to most of the buyers.
  • The installation process is highly simple and quick for almost all aquarium veterans.
  • It does not produce much sound as compared to other models, although it is not entirely silent.


  • If you are new to the use of an aquarium, then definitely installing this will not be easy for you. Usually, it does not come with any setup instruction manual which should be included in it.
  • Many people also say that it, in reality, has an 800 gph flow rate.
  • Moreover, you might have to face some overflow problems during the power outage.

Mainly, here we are discussing the PF-800 overflow box, which is considered as the optimal box for 75 to 125-gallon aquariums as recommended by Eshopps. You can also have a look at the best under tank heater.

The dimensions of this box are 8 by 3 by 10 inches that simply means that there is the need of 3 inches of space between the tank and the wall.

This basically contains the U-tube siphon, pre-filter box, cylinder foams, and other essential items such as wing nuts and nylon screw.

2. Aqueon Hang-On Overflow Box

Aqueon Hang-On Overflow Box, 125-Gallon
  • Any aquarium up to 125 gallons
  • Ready your aquarium for advanced sump filtration
  • No need to empty the aquarium or drill holes
  • Easy to set up, dual drain design in case one gets clogged

Last update on 2021-12-13 / Affiliate links / Images from Amazon Product Advertising API


  • As it offers the capacity of 2200 gph, it is perfect and quite effective to handle return pump flow rates.
  • The setup is not much complicated, which is true for any HOB option.
  • It’s also very good and effective in maintaining siphon.


  • There are few people who do not trust and like the quality of Aqueon. So it is recommended to check first for leaks over the sink before buying. Some other people also complained that after the use of a few years, it falls apart.

This overflow box is basically for 125-gallon tank but the company also offers a 400-gallon version of this box.It is very difficult to do proper and deep research on this as the Aqueon doesn’t provide any detailed description of its features even on its own official website.  

The only information that it gives is its dimensions which are 8.3" x 6.3" x 11.5".Moreover, its design does seem to offer an easy and quick setup as it basically made with a dual drain design. 

The best thing about this box is that if the drains get clogged, it can handle quite a bit of water.

3. KollerCraft TOM RP3 Overflow Box

KollerCraft TOM RP3 Overflow Box
  • Provides easy connection to sump-style filters without aquarium modifications
  • Built-in anti-siphon feature prevents flooding, automatically primes and starts water flow back to filter when electrical power returns
  • Gravity-fed Venturi system automatically primes and initiates water flow to filter sump quickly
  • Capable of handling pumps with up to 800 GPH flow rate
  • Measures 8 x 7-1/2 x 6-1/2 inches (LxHxW); mounts to tank frames up to 1.75 inches thick

Last update on 2021-12-13 / Affiliate links / Images from Amazon Product Advertising API


  • It contains the proper hoses and clamps.
  • It is very easy to set up this overflow box and installation can be done by the beginner tank owners as well.


  • There are also some people who have complained that they do not get the clamps or hoses that should be given with the purchase.
  • Many people also believe that it’s quite overrated in terms of its overall flow rate capacity.

The dimensions of this overflow box are 8 by 7.5 by 6.5 inches (LHW). It is perfect to use for tank frames of maximum 1.75 inches thickness. 

It’s also rated for 800 gph pumps.Moreover, its gravity system primes without any external efforts and specifically in an automatic way. To prevent excessive overflow of water, it also contains an anti-siphon feature.

4. CPR CS90 Overflow Box

CPR CS90 Overflow Box
  • For glass or acrylic aquariums up to 125 gal
  • Flow rate 600 GPH
  • 8" wid
  • 1" bulkhead outflowUL>A built in overflow is the most efficient method of draining aquarium water to
  • Adjustable water level allows you to easily change the level in your tank

Last update on 2021-12-14 / Affiliate links / Images from Amazon Product Advertising API


  • It is absolutely simple to clean and use.
  • It is also very effective in dealing with a power outage.
  • It does not produce much sound.


  • To use this in a proper manner, your return pump should have a flow rate lower than 600gph.
  • To completely maximize its efficiency level, you need to use it with the Aqua Lifter.

This model of overflow box offers 600gph overflow rate and rated for 125-gallon tanks as well. It also provides a quite simple way to adjust the level of water and to prevent the growth of algae; it also contains a black top.

My Pick

In my opinion, all these different types of overflow box work in a proper and effective manner. But if we look for optimal consistency level, then CPR CS90 works great but only if you use the Aqua Lifter pump to with it.

Moreover, it has also received the best reviews from many people. There is hardly any case where you hear about the failure and missing pieces of this box.

Feel free to share your thoughts, submit your questions, and give your valuable recommendations to us.


[Revised and Updated for July, 2019]
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Written by Debra Hutchinson, founder of FishXperts

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