Our picks at a glance
- Best overallAquaClear 50
Large customizable media basket, adjustable flow and a simple, durable design with cheap replacement parts.
- Best featuresSeachem Tidal 55
Self-priming, built-in surface skimmer, adjustable flow and a cleaning indicator in one quiet unit.
- Best budgetTetra Whisper EX 30
Low price, quiet operation and self-priming, a good choice for a first 20 or 30 gallon tank.
- Best multi-stageFluval C3
Five filtration stages including a bio-screen and a chemical stage, with a flow-control dial.
01
What makes a good hang on back filter
A hang-on-back (HOB) filter, also called a power filter, hangs on the rear rim of the tank. An intake tube pulls water up into a box where it passes through media, then it spills back over a lip like a small waterfall. Everything is above the tank, so you can lift the lid and clean it in minutes, and there are no hoses to leak. That simplicity is why HOBs come with so many starter kits and why they remain the best choice for most tanks from 10 to 55 gallons.
The best HOB filters share three traits: a media compartment large enough to hold a real volume of biological media, adjustable flow, and a design that does not force you to throw away bacteria with every cartridge change. Basket-style models such as the AquaClear and Seachem Tidal score highest here, while cartridge models are easier for beginners but hold less media.
If your tank is bigger than about 75 gallons, or you keep large, messy fish, a canister filter usually makes more sense. For a general comparison of every filter type, see our guide to the best aquarium filter.
02
Comparison table
Ratings are manufacturer figures. In practice, most keepers choose a filter rated for 1.5 to 2 times the real tank volume.
| Filter | Rated tank size | Media type | Self-priming | Price |
|---|---|---|---|---|
| AquaClear 50 | 20–50 gal (75–190 L) | Basket, any media | No | $$ |
| Seachem Tidal 55 | Up to 55 gal (210 L) | Basket, any media | Yes | $$ |
| Tetra Whisper EX 30 | Up to ~30 gal (115 L) | Cartridge + scrubber | Yes | $ |
| Fluval C3 | Up to ~50 gal (190 L) | 5 stages | No | $$ |
| Marineland Penguin 350 | ~50–75 gal (190–285 L) | Cartridge + Bio-Wheel | No | $$ |
| Aqueon QuietFlow 30 | Up to ~30 gal (115 L) | Cartridge + bio-holster | Yes | $ |
AquaClear (Fluval) · Customizable media-basket HOB
AquaClear 50
Best for: 20–50 gallon community and planted tanks
The AquaClear line (20, 30, 50, 70 and 110) is the HOB most experienced keepers recommend first. Instead of a disposable cartridge, it uses a deep basket you can fill with the supplied sponge, carbon and ceramic rings, or with any media you prefer. Water flows up through the whole basket, so the media is used efficiently. The AquaClear 50 is rated for 20 to 50 US gallons (75–190 L) with a flow adjustable up to about 200 gph. Downsides: it is not self-priming, so you must fill it after a power cut, and the flow lever can rattle until seated properly.
Pros
- Media basket accepts any media
- Adjustable flow
- Durable, with cheap spare impellers
- Long track record
Cons
- Not self-priming
- Intake can trap fry and shrimp without a sponge guard
- Can be noisy at low water level
- Tank size (maker)
- 20–50 gal (75–190 L)
- Max flow
- About 200 gph (760 L/h)
- Media
- Sponge, carbon, ceramic rings (customizable)
- Other sizes
- 20, 30, 70, 110
Seachem · Self-priming HOB with surface skimmer
Seachem Tidal 55
Best for: Planted and community tanks where convenience matters
The Tidal series (35, 55, 75 and 110) brought several features to the HOB category: a self-priming pump that restarts after a power cut, an integrated surface skimmer that removes the oily film on top of the water, adjustable flow and a maintenance indicator that rises when the media is clogged. The pump sits inside the tank, which keeps it quiet and lets it run even if the water level drops. The Tidal 55 is rated for tanks up to 55 gallons (about 210 L) and uses a large basket that accepts any media. It costs more than an AquaClear and some parts are specific to the model.
Pros
- Self-priming
- Built-in surface skimmer
- Large media basket
- Quiet in-tank pump
Cons
- Higher price
- Pump assembly needs regular cleaning
- Larger footprint behind the tank
- Tank size (maker)
- Up to 55 gal (210 L)
- Max flow
- About 250 gph (950 L/h)
- Extras
- Surface skimmer, cleaning indicator
- Other sizes
- 35, 75, 110
Tetra · Budget cartridge HOB
Tetra Whisper EX 30
Best for: First tanks from 20 to 30 gallons on a budget
The Whisper EX range (20, 30, 45 and 70) is Tetra’s mainstream HOB. It is self-priming, quiet for the price, and uses replaceable Bio-Bag cartridges plus a bio-scrubber grid where bacteria colonize. The EX 30 suits tanks up to about 30 gallons. Cartridges are easy for beginners but you do not need to replace them as often as the box suggests: rinse them gently in tank water and replace only when they fall apart, so the bacteria in the filter are not thrown away each month. The media space is smaller than in an AquaClear or Tidal.
Pros
- Low price
- Self-priming
- Quiet
- Widely available
Cons
- Smaller media volume
- Relies on proprietary cartridges unless modified
- No flow adjustment on some sizes
- Tank size (maker)
- Up to about 30 gal (115 L)
- Media
- Bio-Bag cartridges + bio-scrubber
- Priming
- Self-priming
- Other sizes
- EX 20, 45, 70
Fluval · Five-stage HOB
Fluval C3
Best for: 30–50 gallon tanks where you want chemical media too
Fluval’s C series (C2, C3 and C4) splits filtration into five separate stages: two mechanical (a foam pad and a polyester pad), one chemical (a carbon bag), and two biological (a bio-screen and ceramic media in a trickle chamber). The C3 is rated for tanks up to about 50 gallons. A practical advantage is that you can rinse the mechanical stages without touching the biological ones, so cleaning does not set back your bacteria. The trade-off is that its compartments are fiddly to clean, and some owners find it louder than an AquaClear when the water level is low.
Pros
- Five distinct stages
- Biological media separate from mechanical
- Flow control dial
Cons
- More parts to clean
- Can be noisy at low water level
- Proprietary pads
- Tank size (maker)
- Up to about 50 gal (190 L)
- Stages
- 2 mechanical, 1 chemical, 2 biological
- Flow
- Adjustable
- Other sizes
- C2, C4
Marineland · Cartridge HOB with rotating bio-wheel
Marineland Penguin 350 Bio-Wheel
Best for: Larger community and goldfish tanks up to 75 gallons
The Penguin line is recognizable by its Bio-Wheel, a pleated wheel that rotates in and out of the water. Bacteria on the wheel get plenty of oxygen, which makes biological filtration efficient, and because the wheel is separate from the cartridges, changing a cartridge does not remove most of the bacteria. The Penguin 350 is Marineland’s largest model, aimed at tanks of roughly 50 to 75 gallons, with dual cartridges and dual wheels. The wheel can squeak or stop turning when bearings get dirty, and the cartridge design limits media choice.
Pros
- Very good biological filtration
- Bacteria kept on the wheel during cartridge changes
- Suits larger tanks
Cons
- Wheels can stall or squeak
- Cartridge-based media
- Splashes more, which drives off CO2 in planted tanks
- Tank size (maker)
- About 50–75 gal (190–285 L)
- Biological
- Twin Bio-Wheels
- Media
- Rite-Size cartridges
- Other sizes
- Penguin 100, 150, 200
Aqueon · Quiet cartridge HOB
Aqueon QuietFlow 30
Best for: Bedrooms and living rooms, 20–30 gallon tanks
The Aqueon QuietFlow range is built around low noise: the pump is submerged, and the filter restarts by itself after a power interruption. It uses replaceable cartridges plus a bio-holster that keeps a share of the bacteria when you change the cartridge. The QuietFlow 30 is aimed at tanks up to about 30 gallons. It is a reasonable alternative to the Tetra Whisper, with a red indicator on some models that shows when cartridges need attention. As with any cartridge filter, rinse rather than replace too often, and expect less media room than in basket-style filters.
Pros
- Very quiet submerged pump
- Self-starting
- Bio-holster preserves bacteria
Cons
- Cartridge-based
- Limited media customization
- Impeller needs regular cleaning
- Tank size (maker)
- Up to about 30 gal (115 L)
- Priming
- Self-starting
- Media
- Cartridge + bio-holster
- Other sizes
- 10, 20, 50, 75
03
How we selected these HOB filters
This list is an editorial selection, not a laboratory test. We compared manufacturer-declared tank ratings and flow, the volume and flexibility of the media compartment, self-priming and flow control, the availability of spare impellers and media in the US, and how consistently each model is recommended in established hobby communities. We note known weaknesses, such as noise at low water level or cartridge dependence, so you can weigh them against the price.
04
Buying guide: what to look for
Ignore the gph number on the box as a quality measure. More flow is not better filtration if the media box is small; the water simply rushes through. A filter with a deep media basket and moderate flow usually keeps water clearer and more stable than a fast, shallow one.
- Media capacity and flexibility: a basket that accepts any sponge, floss or bio-media lets you upgrade the filter instead of buying cartridges forever.
- Adjustable flow: essential for betta fish, fancy guppies and shrimp, which struggle in strong current.
- Self-priming: the filter restarts by itself after a power cut. Without it, a non-priming HOB can sit dry and the bacteria start dying within hours.
- Intake guard: fit a sponge pre-filter on the intake to protect fry and cherry shrimp, and to add extra bacteria surface.
- Noise: the waterfall sound rises when the water level drops. Keep the tank topped up, or choose a model with a submerged pump.
- Space behind the tank: HOBs need 4 to 6 inches (10–15 cm) of clearance between tank and wall, plus room for the lid to open.
05
How to choose by tank size
HOB filters shine on 10 gallon to 55 gallon tanks. Use the table below as a starting point and adjust for stocking: heavily stocked tanks and goldfish need a size up, or a second filter.
| Tank | Recommended pick | Notes |
|---|---|---|
| 5–10 gal (20–40 L) | AquaClear 20 or Seachem Tidal 35 | Turn the flow down for bettas |
| 20 gal (75 L) | AquaClear 30 or Tetra Whisper EX 30 | Add an intake sponge for small fish |
| 29–40 gal (110–150 L) | AquaClear 50 or Fluval C3 | Good fit for most community tanks |
| 55 gal (210 L) | AquaClear 70, Tidal 75 or two smaller HOBs | Two filters spread maintenance |
| 55–75 gal goldfish (210–285 L) | AquaClear 110 or Penguin 350 | Or switch to a canister |
On a 20 gallon tank, an AquaClear 30 or 50 with the flow turned down gives you extra media capacity without creating a whirlpool.
06
Setting up and maintaining an HOB
Installing a hang-on-back filter takes minutes, but a few habits make the difference between a filter that runs quietly for years and one that rattles and floods.
- Rinse sponges and media in dechlorinated or tank water, then place them in the basket in this order from bottom to top: sponge, bio-media, fine floss if you use it.
- Hang the filter level on the rim and push the intake tube down to about 2 inches (5 cm) above the substrate.
- Fill the box with tank water before plugging in, unless the model is self-priming.
- Seed the filter with a squeeze of an established sponge or a bottled bacteria product, then follow a proper fish tank cycle.
- Every 2 to 4 weeks, rinse the sponge in old tank water during your water change, and clean the impeller every 2 to 3 months.
Never replace all the media at once. If a cartridge must be replaced, keep the old one in the filter for 2 to 3 weeks alongside the new one, or keep a separate sponge, so the bacteria colony survives.
07
Common mistakes with hang on back filters
If the water stays hazy weeks after setup, check feeding and stocking before blaming the filter. Our guide to cloudy fish tank water covers the usual causes, and how to clean a fish tank explains how to schedule filter cleaning around the rest of your maintenance.
- Changing cartridges every month. The box says so, but it throws away beneficial bacteria. Rinse, do not replace, until the media falls apart.
- Letting the water level drop. A big gap between the outflow and the water surface causes noise and splashing.
- Not leveling the filter. A tilted box can overflow behind the tank.
- Ignoring the impeller. Most noise and flow loss come from a dirty impeller or worn shaft, not from the motor.
- Using carbon permanently. Activated carbon is useful after medication, but it exhausts in a few weeks and is not needed in a healthy tank.
Frequently asked questions
Frequently asked questions
What is the best hang on back filter for a 20 gallon tank?
The AquaClear 30 or AquaClear 50 is the most popular choice for a 20 gallon tank because of its large, customizable media basket and adjustable flow. The Seachem Tidal 35 is a self-priming alternative. On a budget, the Tetra Whisper EX 30 is quiet and dependable.
Are HOB filters good enough for a 55 gallon tank?
Yes, for a moderately stocked community tank. Use a large model such as the AquaClear 70 or 110 or the Seachem Tidal 75, or two medium HOBs on each side of the tank. For goldfish, big cichlids or heavy stocking, a canister filter is a better fit.
How often should I clean a hang on back filter?
Rinse the sponge in old tank water every 2 to 4 weeks, or when flow visibly drops. Clean the intake tube and impeller every 2 to 3 months. Replace media only when it is falling apart, and never all at once.
Why is my HOB filter so loud?
The most common causes are a low water level, which makes the outflow splash, and a dirty or worn impeller, which rattles. Top up the tank, clean the impeller well, and check the filter is level. If the noise remains, replace the impeller assembly.
Do hang on back filters work for bettas and shrimp?
They can, with adjustments. Turn the flow to its lowest setting, fit a sponge pre-filter over the intake so fins and shrimp are not pulled in, and break the outflow with a plant or the glass. A sponge filter is still the gentlest option for small betta tanks.
Sources and references
Written and reviewed by the handsoffmyhobby editorial team according to our editorial policy.
