Adding a sump to your aquarium is one of the best ways to improve filtration, hide equipment, and increase overall water volume. The only problem is that not every tank comes drilled and ready for one.
That’s where an aquarium overflow box comes in. These handy devices let water move from your display tank down into a sump without needing to drill the glass. They are especially useful if you want to upgrade a standard aquarium into a more advanced reef or freshwater setup.
In this guide, we’ll look at some of the best aquarium overflow boxes, including compact options, high-flow models, and hang-on-back designs for different tank sizes.
Aquarium Overflow Box
If you plan to set up a sump, an overflow box will be an excellent entry point. It allows you to transfer the aquarium water to the sump underneath the cabinet. At the same time, you can easily install wet and dry filtration systems to keep your tank in excellent condition.
The type that you need will depend on a variety of factors from:
- The type of fish you are keeping
- The size of your tank
- What other filtration and tank care devices you already have set up
For example, if you are already using a dosing pump, that might affect which overflow you get. Make sure you read the reviews of those who have tried and tested these overflow boxes in order to get the full picture of capabilities and best use cases.
1. Blue Ocean Overflow Box
The Blue Ocean Overflow Box is a simple hang-on-back option for aquarists who want to connect a sump without drilling their tank. It has a continuous siphon design and is built from acrylic, giving it a clean and practical setup for standard aquariums.
This model is rated for around 600 GPH and is suitable for tanks up to about 125 gallons. It also includes a 1-inch bulkhead and works with standard 1-inch PVC, which makes plumbing it into a sump system fairly straightforward.
One thing to note is that this overflow box does not use traditional U-tubes. That can make the design feel a little cleaner, but it may also need a powerhead or air-lift pump to help prevent air from building up and breaking the siphon over time.
Overall, the Blue Ocean Overflow Box is a good mid-range choice if you want a basic, affordable overflow box for a medium-sized aquarium.
Pros:
- 600 GPH flow rate
- Good for tanks up to 125 gallons
- No drilling required
- Includes 1-inch bulkhead
- Works with standard PVC
Cons:
- May need a powerhead to maintain siphon
- Manual may not be included
- Not as polished as premium overflow boxes
2. Seapora Overflow Prefilter
The Seapora Overflow Prefilter is a low-profile acrylic overflow box designed to turn a regular aquarium into a reef-ready style setup. It hangs on the back of the tank and moves water down to your sump using a U-tube design.
One of the nice things about this range is that it comes in several sizes, including models rated for 300 GPH, 800 GPH, 1000 GPH, and 1200 GPH, depending on the tank size you need to support. The Seapora 300 model, for example, is suited for tanks up to 75 gallons.
It also includes useful starter parts like foam cylinders, a nylon U-tube, and a bulkhead, so it gives you most of the core pieces needed for a basic overflow setup.
Overall, the Seapora Overflow Prefilter is a solid pick if you want a straightforward hang-on overflow box with multiple sizing options.
Pros:
- Low-profile acrylic design
- Several flow-rate options
- Includes U-tube and bulkhead
- Good for converting standard tanks
- Available for small to larger aquariums
Cons:
- U-tube needs proper setup and maintenance
- Exact size depends on the model
- Not as compact as some newer designs
3. Eshopps PF-1200 Overflow Box
The Eshopps PF-1200 is a stronger option for larger aquariums that need more water movement between the display tank and sump. It’s a hang-on-back overflow box, so it lets you add sump filtration without drilling your aquarium.
This model is rated for up to 1200 GPH and is designed for tanks around 150 to 200 gallons. It uses a dual-intake setup and includes 1-inch bulkhead fittings, making it a good choice for larger reef tanks or heavily stocked systems.
Eshopps also designed the PF series with a slimmer internal pre-filter box, which helps reduce the amount of space it takes up inside the aquarium. The recessed cover on the outside box can also help reduce splashing and noise compared to more basic overflow boxes.
Overall, the Eshopps PF-1200 is one of the better choices if you need a high-flow overflow box for a larger tank and want something more refined than a budget model.
Pros:
- High 1200 GPH flow rate
- Good for 150–200 gallon tanks
- Dual intake design
- Slimmer internal pre-filter box
- Designed to reduce splashing and noise
Cons:
- More than most small tanks need
- Takes more setup space than compact models
- Usually costs more than basic overflow boxes
Types of Overflow Boxes
There are several types of aquarium overflow boxes, and some of them don’t require drilling the glass.
This is why you need to be careful about the type and size of the overflow box before buying one to install it in your tank.
1. Internal hang-on overflow boxes
These are the most straightforward models to install, so they will work better if you’re a beginner or you don’t have a big aquarium that you’re trying to manage.
However, these models are most likely to fail. They usually fail when the siphon stops working because of a power outage or the failure of pumps and tubes.
If you’re on a tight budget, this overflow box will work for you because you can install it without drilling the glass. You can also overcome its failure points by building a larger sump.
2. Internal built-in overflow box
If you’re looking for something more advanced, you need to invest in an internal built-in overflow box.
This is the overflow box that you’re likely to see on reef-ready systems.
The overflow box is integrated into the body of the tank and is more expensive.
3. External overflow box
Serious aquarists and those who are willing to make the biggest investments should invest in an external overflow box.
There are currently compact designs that have a small footprint inside your tank, and would still perform exceptionally to keep your aquarium in perfect condition.
There are 2 disadvantages associated with this type of overflow box:
- The first one is that you can’t install your aquarium to the wall because your overflow box will stick out
- The second one is that you will have to drill the glass or hire someone to drill it before you’re able to install the overflow box
For these reasons, many choose one of the other two styles.
Fish Tank Overflow Box Size
Overflow boxes are self-regulating, and this means that they won’t drain more water than the amount that flows into them.
This is why you need to make sure that the overflow box you’re picking is suitable for the return pipe you’re buying.
You can start by shopping for the return pump and then buy an overflow box with a flow rating higher than that of the pump.
If you’ve already picked a box, make sure that the return pump you pick is rated lower than the flow rate of the box.
You can also calculate the adequate size by taking the size of the aquarium and multiplying it by 10. After that, you can round the number to the nearest number that exceeds the result.
For example, if you have a 55-gallon tank, you multiply this number by 10 and get an overflow box that is rated higher than 550gph.