Best Hang-On-Back (HOB) Protein Skimmers for Reef Tanks
You probably already know that a protein skimmer can be one of the most useful pieces of filtration equipment you can add to a saltwater aquarium. But, unfortunately, not every aquarium has room for a sump. That's where hang-on-back (HOB) protein skimmers come in. Like the name suggests, these skimmers hang directly on the back rim of the aquarium, giving reefers a way to remove dissolved organic waste before it breaks down into nitrate and phosphate. No drilling your tank or plumbing a sump required.
Before choosing a HOB skimmer, it helps to know what actually matters. Tank size ratings are useful, but they're not the only thing to consider.
Recommended tank size
Always look at the bioload ratings when available. A skimmer rated “up to 75 gallons” may be better suited for a smaller reef tank with a heavy fish load. While these are somewhat subjective, they're a good rule of thumb. Bigger isn't better when it comes to skimmers, and it's often better to undersize a skimmer slightly. An oversized skimmer can be hard to tune and perform inconsistently.
Footprint and clearance
HOB skimmers need space behind the aquarium, inside the tank, and above the tank to remove the collection cup. This matters a lot if your aquarium is close to a wall or tucked under a cabinet. Choose a low-profile option if you're tight on space.
Pump quality
A good needle wheel pump is what creates the fine bubbles that make protein skimming work. Many of these skimmers use modified Sicce/Shark-style pumps, which are known for reliable skimmer performance.
Ease of maintenance
Collection cup access, removable parts, and easy pump cleaning all matter. A skimmer that's hard to clean is a skimmer that eventually gets neglected. Thankfully, all the skimmers on this list are easy to clean and come nearly fully apart for easy access.
In this guide, we've broken HOB protein skimmers down into four categories: Best Overall, Best Low-Profile Design, Best for Larger Reef Tanks, and Best Skimmer & Filtration Combo. With several options to choose from, you're sure to find the right skimmer for your setup here.
Best Overall
HOB-1.5 Hang-on-Back Protein Skimmer
The AquaReady HOB-1.5 Protein Skimmer is first up on the list because it's been a favorite in the reefing hobby for years, which explains why it's our best selling HOB skimmer option.
This is the option that's generally the “best all-around” pick for reefers who want a traditional HOB protein skimmer that is simple, effective, and well sized for many common reef tanks.
Best For: Medium size saltwater aquariums without a sump.
Recommended Tank Size:
- Heavy Bioload: 40 Gallons
- Medium Bioload: 60 Gallons
- Light Bioload: 75 Gallons
Pump: Sicce Shark 1.0
Max Rim Thickness: Up to 3/4"
Best Low-Profile Option
Bullet Hang-On-Back Protein Skimmers
The Bullet lineup of skimmers are becoming increasingly popular with their low-profile design and black color scheme. Unlike many HOB protein skimmers that can be bulky and unsightly, the Bullet skimmers have a small footprint, meaning they won't stick up above the tank rim as far and don't require as much space between the aquarium and wall behind it.
They're largely made from black acrylic, allowing them to more easily blend in and go unnoticed. And thanks to the modified Sicce pump and built-in air silencer, you'll hardly know it's even running.
Best For: Small to medium size reef tanks where both performance and a low-profile form factor are important.
Bullet-1 Hang-On-Back Protein Skimmer
Shop NowRecommended Tank Size:
- Heavy Bioload: 20 Gallons
- Light Bioload: 30 Gallons
Pump: Sicce Shark Nano
Max Rim Thickness: 3/4"
Bullet-2 Hang-On-Back Protein Skimmer
Shop NowRecommended Tank Size:
- Heavy Bioload: 30 Gallons
- Light Bioload: 50 Gallons
Pump: Sicce Shark 0.5
Max Rim Thickness: 3/4"
Bullet-3 Hang-On-Back Protein Skimmer
Shop NowRecommended Tank Size:
- Heavy Bioload: 40 Gallons
- Light Bioload: 80 Gallons
Pump: Sicce Shark 1.0
Max Rim Thickness: 1"
Best for Larger Reef Tanks
ConeS HOB Hang-On-Back Protein Skimmer
The ConeS HOB Hang-On-Back Protein Skimmer is the heavy-hitter on this list. It is designed to bring cone-style skimmer performance to tanks without a sump, making it a strong choice for reefers who want more aggressive nutrient export from a hang-on-back setup.
The ConeS HOB is commonly listed for tanks up to 175 gallons and uses a modified Sicce/Shark pump with a needle wheel design. It also includes a conical diffuser or hybrid cone-style body designed to stabilize flow and help improve foam production.
Best For: Larger reef tanks and for reefers who want something closer to in-sump skimmer performance but still need a hang-on-back format.
Recommended Tank Size:
- Heavy Bioload: 90 Gallons
- Medium Bioload: 130 Gallons
- Light Bioload: 175 Gallons
Pump: Sicce Shark 1.5
Max Rim Thickness: Up to 3/4"
Best Skimmer & Filtration Combo
HF-M Complete Filtration System
The HF-M Complete Filtration System is completely different than everything else on our list because while it is a hang-on option and includes a protein skimmer, it also has space for additional mechanical, chemical, and biological filtration.
Using the HF-M means less gear hanging on the back of your tank as it often replaces the need for additional HOB power filters, media reactors and even probe holders. The nearly all-black acrylic construction adds to the sleek look.
Best For: Reefers who want a complete filtration system and less gear hanging on the back of their tank.
Recommended Tank Size:
- Heavy Bioload: 20 Gallons
- Medium Bioload: 40 Gallons
- Light Bioload: 60 Gallons
Pump: Sicce Shark 1.0
Max Rim Thickness: 3/4"
Frequently Asked Questions About HOB Skimmers
How do I know what size HOB protein skimmer to buy?
The best place to start is looking at the manufacturer's recommendations. Each skimmer will typically have a recommended tank size range.
Tanks with more waste to export will require a larger skimmer and tanks with less waste can get by with a smaller skimmer, so there isn't a one-size-fits-all answer.
If you have a lot of fish and corals and feed heavily, go with the heavy bioload recommendation. If you have just a few fish and don't plan to add much more, the light bioload is a good option. Most reefkeepers will fall somewhere in the middle of this recommended range.
Should I size my skimmer based on tank gallons or bioload?
Tank size based recommendations are a good starting point, but how many fish and corals you have in your aquarium (often called bioload) will greatly impact which skimmer you should choose.
Many skimmers will list a suggested tank size, but based on stocking level in the aquarium. This is slightly subjective, but it's a good reference point when picking a skimmer.
Can a HOB protein skimmer be too big for my aquarium?
Yes! This is one of the most common mistakes we see hobbyists make. With protein skimmers, bigger isn't better.
When a Skimmer is Too Large
If your skimmer is too large for your tank and bioload, it can be hard to tune, resulting in inconsistent performance. One minute it's pulling skimmate, the next it's seemingly not working. Then suddenly, it's overflowing.
When a Skimmer is Too Small
An undersized skimmer is typically easy to tune and consistently pulls organics from the water. Even if it's not optimal like a properly sized skimmer would be, under sizing a skimmer is much preferred compared to oversizing one.
Will a HOB protein skimmer fit on a rimmed aquarium?
In most cases, yes.
Most HOB skimmers are designed for smaller to medium sized aquariums, so they may not fit on larger tanks with a thick rim. Hang-on skimmers will typically have a maximum rim thickness listed, so it's always wise to double check dimensions before buying.
How long does it take for a new protein skimmer to break in?
Usually less than a week.
New plastics, acrylic, tubing, and pump parts can cause unstable foam for the first few days.
If you take the time to thoroughly rinse the skimmer before use, you'll notice consistent results more quickly.
Why is my protein skimmer overflowing?
A skimmer might overflow for several reasons, but here are some of the most common causes:
- New skimmer break-in period: New plastics, acrylic, tubing, and pump parts can cause unstable foam for the first few days.
- Water level is too high: If the internal water level is too high, the skimmer can push water into the collection cup instead of foam.
- Recent additives or chemicals: Water conditioners, medications, epoxy, coral glue, bacterial additives, and some foods can make a skimmer overflow.
- Improperly tuned: Running the skimmer too “wet” can cause the cup to fill quickly with watery skimmate.
Learn More: Top 5 Protein Skimmer Fixes
Why is my protein skimmer not producing foam or skimmate?
If your skimmer isn't producing any bubbles at all, air not getting to the pump is almost always the problem.
- Inspect the airline tubing for any obstructions
- Inspect the venturi for clogs (often caused by precipitation due to two-part dosing)
If your skimmer is producing foam, but nothing is getting collected in the collection cup (typically called skimmate), there could be a few reasons for this, including:
- Water level is too low: If the internal water level is too low, the skimmer pump won't be able to push the water/foam mixture up high enough to overflow into the collection cup.
- Bioload too light/skimmer oversized: If there aren't any organics in the water to remove, the skimmer won't produce any skimmate.
- Pump is dirty: If the skimmer pump is dirty, it may not be pushing enough water to create a proper foam head in the skimmer neck.
- Improperly tuned: Running the skimmer too "dry" can result in waste collecting in the skimmer neck, but never reaching the collection cup.
Learn More: Top 5 Protein Skimmer Fixes
How often should I clean a hang-on-back protein skimmer?
The most important part to clean regularly is the skimmer cup and skimmer neck. Cleaning these once a week is usually sufficient.
A full tear-down cleaning should only be needed every few months.
If you notice fewer bubbles in the skimmer than normal, check to make sure the venturi isn't clogged and give the pump a good cleaning.
Adam has been reef keeping since 2010 and got his start on the Bulk Reef Supply Customer Service team. He believes the best tanks are built around what you enjoy, not what’s trending. Adam is especially interested in simplifying the hobby, exploring the latest gear, and helping others focus on long-term success over chasing perfection.
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