Anyone keeping a reef aquarium knows a protein skimmer is important for maintaining good water quality. No serious reef keeper would be without a protein skimmer.
But what if you don’t have a sump or room under your tank for a protein skimmer? The good news is that there are Hang On Back (HOB) protein skimmers that are easy to install and don’t require a sump or to be positioned under the aquarium.
We’ll review the top HOB protein skimmers you should consider for your reef aquarium. But first, let’s look at what a protein skimmer does and why you need one.
Dissolved organics in the reef aquarium
A natural reef is continuously flushed clean with millions of gallons of seawater.
Reef tanks are closed aquatic systems. This means some substances will accumulate in the water.
All aquarium life releases dissolved organic compounds (DOC) into the water. Algae contain oils that leak out of living cells and also when the algae die. Soft and hard corals periodically shed their mucus coating. Marine fish continually produce a new mucoprotein slime coat to replace what gets rubbed off. Invertebrates release dissolved and solid waste. Even bacteria contribute to the organic load in the aquarium.
In the oceans, these natural wastes get flushed away and recycled. Not so much in our aquariums.
The dissolved organics tend to build up in the aquarium water. Dissolved organics cause a yellow tint that absorbs blue light energy.
Blue light is important for photosynthesis in most reef corals.
Dissolved and solid particulate organic waste is food for heterotrophic bacteria. While heterotrophic bacteria are beneficial and essential to your reef aquarium’s ecosystem, having too many is not helpful.
Supplying the bacteria with a lot of food (organics) causes the population to grow to unnaturally high levels. This disrupts the natural microbe balance in the reef tank.
Aquatic research revealed that excess organics promote harmful pathogenic bacteria in aquariums. Some organic substances can decompose and be converted into ammonia, nitrite, nitrate and algae-promoting phosphate.
A protein skimmer will pull these organics out of the water before they can cause problems in your aquarium.
How Do Protein Skimmers Work?
Aquarium protein skimmers are designed around a special separation process called foam fractionation.
The technique was invented to remove surface active (foam forming) substances from a liquid, by physically removing it as a foam. By agitating the liquid the surface active substances form a foamy mass that can be separated (skimmed) from the liquid.
Aquarium protein skimmers use the same process but on a smaller scale.
Dissolved organic carbon in aquarium water will foam up if the water is continuously agitated. But it’s not that simple.
Protein skimmers work by creating a rising column of air bubbles inside the skimmer body. As the air bubbles rise, the dissolved organics attach to the bubble surface and are carried to the top of the protein skimmer.
When the bubble bursts the DOC is released as foam. But since the skimming process is continuous the foam continues to build up inside the skimmer.
Eventually, the foam rises and is captured in the collection cup. The dissolved organics are now removed from the aquarium water.
Not every pollutant is surface active, however. A protein skimmer can only remove substances that foam up.
Ammonia and nitrite, for example, are inorganic substances. They don’t foam and can’t be removed by a protein skimmer.
The goal of skimming is to remove these organics before they can be decomposed and end up as nitrate and other pollutants.
Protein skimmers indirectly lower ammonia, nitrite, nitrate and algae-promoting phosphate and improve water quality by stripping out organic pollutants from your aquarium water.
Do I really need a protein skimmer?
If you don’t have a protein skimmer on your saltwater or reef tank you may wonder if it’s really necessary. Consider these benefits to running a protein skimmer on your tank:
- Sparkling clear water with no yellow tint,
- Better light penetration throughout the aquarium,
- Full spectrum light energy available to the corals,
- Better coral growth and reproduction,
- Corals recover faster when fragging,
- Less chance of disease problems when propagating frags,
- More colorful corals due to improved photosynthesis,
- Less bioload from heterotrophic bacteria,
- Less algae on your live rock due to nutrient reduction in the water,
- Aquarium glass will stay cleaner longer – less algae scrapping,
- Less red slime (cyanobacteria) problems,
- Fish stay healthier through improved water quality,
- Less nitrate in the water.
As this list demonstrates, there are many benefits to adding a protein skimmer to your reef or fish-only aquarium.
We’ve evaluated the top Hang On Back (HOB) protein skimmers so you can make an informed decision when selecting a skimmer for your tank.
High-rated HOB Protein Skimmer Reviews
1. CPR Bak-Pak 2
CPR Aquatics is a well-established aquarium equipment manufacturer.
CPR was one of the first companies to design and manufacture a hang on back protein skimmer.
The CPR Bak-Pak 2 is a second generation HOB protein skimmer.
It provides protein skimming and biological filtration in one unit. Water is pumped from the aquarium into the skimming chamber.
The water flows downward in the skimming chamber while the venture system injects air at the bottom. This increases contact time with the air bubbles and makes the protein skimmer very efficient.
The smoke-colored skimmer collection cup height is adjustable. This allows you to slide it up or down depending how wet the foam is. Some aquarists find this method to be an easier adjustment process than having to regulate water valves and pump flow rate.
The water leaves the skimmer and passes through a second chamber containing CPR’s Bio-Bale biological filtration media before returning to the aquarium.
Like the original model, the Bak-Pak 2 is rated for aquariums up to 60 gallons.
The new design features an easier to clean intake system and an enclosed outflow tube. The new outflow tube creates less salt spray and helps to eliminate fine bubbles from entering the aquarium.
The Bak-Pak 2 measures 7.5 inches wide, 3 inches deep and 17 inches tall.
- High-quality craftsmanship.
- Low defect rate.
- Proven to last many trouble-free years.
- Plug and play simplicity.
- Very effective protein skimming.
- The air intake is noisier than other brands.
2. AquaMaxx HOB-1.5
The AquaMaxx HOB protein skimmer has undergone a recent design upgrade.
A larger collection cup has been added along with a silicone drain elbow.
Management of the
The HOB-1.5 uses an upgraded Italian Sicce Syncra pump for quiet, reliable service.
The water pump is located inside the skimmer. The water pump draws in air and mixes it with the water. AquaMaxx has a unique bubble plate that fires the air/water mix into the skimmer body.
The AquaMaxx HOB-1.5 is rated for tanks up to 90 gallons with a light bioload.
Tanks in the range of 40-50 gallons with a heavy bioload are probably the largest size this skimmer can handle. The dimensions are 7.5 wide, 3.5 inches deep and 17 inches tall.
The maximum rim thickness the hanger can accommodate is ¾ inches.
- Simple plug and play operation.
- Improved stronger hanger bracket.
- Larger skimmer cup.
- One-year manufacturer’s warranty.
- Somewhat weak construction (recently upgraded hanger).
- Uses common plumbing fittings.
3. CoralVue Reef Octopus Classic 100 HOB
CoralVue’s Reef Octopus line of protein skimmers are well-known by reef enthusiasts worldwide.
CoralVue took their big skimmer know-how and built a powerful hang-on-back protein skimmer for aquarists who can’t have a sump or stand-alone skimmer.
The Reef Octopus design places the water pump under the skimmer, outside of the aquarium.
This design takes up less room in the aquarium because there is no bulky water pump hanging in your tank. Instead of transferring pump heat to the aquarium, the Reef Octopus external pump design allows heat to transfer to the air.
This will reduce the chances of overheating in the aquarium and make it easier to keep water temperature under control.
This protein skimmer is rated for tanks up to 130 gallons (light bio-load) but typically used on aquariums up to 75 gallons. Dimensions are 8 inches wide, 3.5 inches deep and 17” tall.
- Low profile design.
- Comes with an Aquatrance 1000s water pump.
- Uses a surface skimmer.
- Reduces noise with an air silencer.
- External water pump for heat transfer.
- Produces a good quantity of skimmate.
- Installation instructions could be better.
- Attention must be paid to proper O-ring seating to avoid leaks.
4. Coralife Super Skimmer
The Coralife Super Skimmer is an HOB-type protein skimmer that can also be used in a sump.
Three models are available for tanks up to 65, 125 and 220 gallons.
Coralife Super Skimmers feature a patented needle-wheel water pump system.
The aspirating venturi injects micro-bubbles that rise, dragging dissolved organics with them to the collection cup.
The Super Skimmer design has angled dual injection outlets intended to increase contact time inside the reaction chamber. Water height and foam production are adjustable by using the water-level dial.
The integrated bubble diffuser prevents microbubbles from flowing into the aquarium. The collection cup twists off for cleaning.
Models 125 and 220 have a collection cup drain option for quick and easy cleaning. High-grade acrylic construction. Includes everything for convenient hang-on or in-sump setup.
- Poor set-up and use instructions.
- Product manual does not match the skimmer.
- The skimmer requires extensive adjustment every time it is restarted.
- Has a reputation for overflowing and flooding.
- Bulking design takes up more room than other brands.
5. Eshopps Hang On PSK-75H
Eshopps is another well-respected aquarium equipment manufacturer.
The PSK-75H model is made for marine aquariums up to 75 gallons.
The acrylic construction will give years of trouble-free operation. The cylinder body is three inches in diameter.
The skimmer footprint measures 7 inches by 6 inches.
The water pump is positioned under the skimmer, outside of the aquarium. This takes up less space inside the aquarium and reduces heat transfer into the water.
Eshopps uses a high-quality Italian water pump manufactured by Sicce. The water pump uses a needle-wheel impeller and venturi system to inject microbubbles into the water.
The collection cup is removable for easy cleaning. You have the option of using cup drain option.
- Quiet operation.
- Known for reliability.
- Simple installation.
- External water pump does not heat the aquarium water.
- Has a bubble plate to reduce microbubbles in the aquarium.
- Older models had a problem with an unreliable water pump.
6. Bubble Magus QQ1 Hang-On Nano
The Bubble Magnus QQ1 has the look of a small hang on the back power filter, but the QQ1 is designed strictly for protein skimming on nano reef aquariums.
Rated for reef aquariums up to 25 gallons, this little skimmer hangs on the side or back of the aquarium, like a power filter.
A Rock SP600 water pump with a special needle wheel impeller draws in aquarium water and infuses it with tiny air bubbles.
The agitated water forms a protein froth that rises into the skimmer cup. You can adjust the skimmate by raising or lowering the height of the collection cup. The plastic thumbscrew holds the cup at the desired height. To clean the cup, simply remove it from the main skimmer body.
The Bubble Magnus QQ1 even has an air silencer to reduce noise and a basic bubble diffuser plate to increase performance. The unit measures 5.8"L x 4.4"W x 10.5"H.
- Easy to install.
- Simple adjustments.
- Entire unit can be carried to the sink for cleaning.
- Relatively quiet operation.
- Does not create microbubbles in the aquarium.
- Won't fit on glass thicker than 12 mm (about ½”).
- Plastic may crack if the thumbscrew is over-tightened.
- A little too bulky to hang on the side of a small tank.
- Won't work with AIO filters.
Hang-On Protein Skimmers Recommendations
We’re pleased to report that you have several high-quality HOB protein skimmers to choose from in our evaluation. One of the important observations we want to pass on to you is that you should make sure any fittings are hand-tightened before you fill the skimmer with water. Plastic fitting can become loose during shipping so please check before putting the skimmer in operation. You only need to hand-tighten, don’t use a wrench. If you see a
Also, note that new protein skimmers do not immediately make foam and
It normally takes a couple of days for the skimmer to “break in” and start making foam.
Our favorite is the AquaMaxx HOB 1.5. AquaMaxx has been manufacturing hang-on-back protein skimmers since 2010. They’ve introduced unique skimmer innovations that are known for effectiveness and reliability. The AquaMaxx HOB 1.5 is an upgrade from the previous version for more powerful efficiency with no sacrifice on quality or performance. Unlike the Coralife Super Skimmer, which is difficult to set up and keep running consistently, the AquaMaxx HOB 1.5 performs flawlessly.
A close second is the Eshopps Hang-On. Like CPR, Eshopps has been making protein skimmers for a long time. The original Hang On skimmer had a problem with the water pump but has been corrected on the updated model. The Eshopps design has been proven to work well over many years it has been on the market.
Aquarists can have confidence that an Eshopps protein skimmer will work as intended and keep their tanks clean and healthy.
Still not found your new skimmer? Have a look at my selection of nano skimmer for small tanks or nine of the quietest protein skimmers compared.
Share your ideas in the comment section just below, thank you!
I have a 30-gallon aquarium. It’s been running for 3 months now. It has fish, invertebrates, and an anemone and we want to add corals in the near future. Do you recommend CPR Bak-Pak 2 Protein Skimmer as my only filtration for the aquarium?
The CPR Bak-Pak 2 is a fine skimmer. But it won’t remove a lot of particulate matter. A simple hang on the back power filter can be used to capture debris and provide a place to use specialty media like phosphate removers or activated carbon.
Ever heard of using 100% wool as a media for aquariums?
Sheep’s wool is being used for air filtration and building insulation. But natural wool contains lanolin, a wax secreted by the sebaceous glands of sheep. That’s not something you want in your aquarium. Polyester fiber is used in many aquarium filters and as loose “wool-like” filter floss. Change it out every few weeks to keep it from clogging.