Last Updated on October 12, 2025 by Donna Williams
The Great Filter Debate: Hanging On or Tucking In?
So you’ve got a small aquarium. Maybe it’s a sleek 10gallon on your desk or a cozy 5gallon betta palace. You’re past the bowl stage (thank goodness), and now you’re staring down the filter aisle or an endless scroll of online options. And you’re stuck on the big question: Do you go with the classic hangonback (HOB) filter or the neat little internal one that hides inside the tank?
I’ve been there. I remember setting up my first “real” tank, a 20gallon long, and spending an entire afternoon paralyzed by this choice. I went with an internal filter because it looked cleaner. And then I spent the next six months fighting with it during every water change, cursing the bulky thing taking up my aquascaping space. Trust me on this one, the right choice matters more than you think.
Let’s break this down, not with confusing jargon, but like two fishkeeping friends comparing notes. We’ll look at the pros, the cons, and the realworld stuff the box never tells you.
Meet the Contenders: A Quick Intro
First, let’s be sure we know what we’re talking about.
A HangOnBack (HOB) Filter, sometimes called a power filter, does exactly what its name says. It hangs on the back lip of your aquarium. Water is pulled up a tube, pushed through filter media (sponges, carbon bags, etc.), and then spills back into the tank like a gentle waterfall.
An Internal Filter is a selfcontained unit that sits fully inside your tank, usually suctioncupped to the glass. It pulls water in through slots, pushes it through an internal cartridge or sponge, and spits it back out, often with a spray bar.
Simple enough, right? Here’s where it gets interesting.
The HOB Filter: The TriedandTrue Workhorse
HOBs are the old reliables of the aquarium world. Brands like AquaClear and Seachem Tidal are legendary for a reason. They just work.
Why you might love a HOB:
- Maximizes Tank Real Estate: This is huge for small tanks. Every square inch counts. By living on the outside, a HOB gives your fish and plants all the internal space. No bulky plastic box ruining your underwater zen garden.
- Superior Gas Exchange: That waterfall action? It’s not just for looks. It violently agitates the surface, which is the primary way oxygen gets into your water and CO2 gets out. This is a massive, often overlooked benefit, especially in warmer water where oxygen levels can drop.
- Easier Maintenance: You don’t have to stick your entire arm in the tank to get the filter. You just lift the whole box off the back, open the lid, and swap or rinse the media. It’s a 2minute job that doesn’t disturb your fish or your hardscape.
- More Media Space: HOBs typically have a larger basket, allowing you to customize your filtration. You can add a coarse sponge, a bag of Purigen, some filter floss, and still have room for activated carbon if you need it. This flexibility is a gamechanger for water clarity.
And the potential downsides:
- The Noise Factor: That soothing waterfall sound can, for some people in a quiet bedroom, become a distracting gush. Newer models are much better, but it’s a consideration.
- Potential for Flooding: If the water level drops too low (from evaporation), the pump can run dry and burn out. Or, if the intake tube gets clogged, the motor can sometimes push water out of the back of the unit. It’s rare, but it happens.
- Look isn’t for Everyone: Some folks just don’t like the look of equipment hanging off their tank. They want a completely selfcontained view.
Here’s a pro tip from my own experience: If you go the HOB route, spend the extra few bucks on a prefilter sponge. It’s a little sponge that slides over the intake tube. It protects baby fish and shrimp from being sucked in, and it’s the first line of mechanical filtration, making your main media last way longer. Seriously, it’s the best $3 you’ll ever spend.
The Internal Filter: The Stealthy Submersible
Internal filters are the ninjas of filtration—out of sight, out of mind. They’re popular for nano tanks and betta setups where the current needs to be minimal.
Why an internal might be your jam:
- Clean, Unobstructed Look: This is their biggest selling point. From the front and sides, your tank looks pristine. No cords or boxes hanging off the back. It’s all about the illusion of a natural, selfsustaining ecosystem.
- Absolutely LeakProof: It’s already in the water. It can’t leak onto your floor or cabinet. This peace of mind is a big deal for a lot of people.
- Great for LowFlow Situations: Many internal filters have an adjustable flow or are inherently gentle, making them perfect for fish that hate current, like bettas, fancy guppies, or dwarf puffers.
- Simplicity: They are often very simple devices. Plug it in, stick it in, and you’re done. No priming, no worrying about water levels.
And the notsogreat parts:
- It Eats Up Your Precious Space: In a 5gallon tank, a filter that’s 6 inches long and 2 inches wide is a significant chunk of your swimming and planting area. It can be a real pain to hide with plants and decor.
- Maintenance is a Hassle: To clean it, you have to reach into the tank, pull out a slimy, algaecovered box, and open it—usually releasing a cloud of gunk into your water. It’s a much messier, more disruptive process.
- Limited Media Capacity: Most internal filters rely on a single, small cartridge or a tiny sponge. There’s little room for customization or adding specialized chemical media.
- Can Be an Eyesore Inside: While hidden from the outside, you still have to look at it inside the tank. And they often grow algae, which can make them look unkempt.
Funny story: I once had an internal filter in a shrimp tank. The shrimp loved to breed inside the filter casing, using the calm, foodrich environment as a nursery. It was great until maintenance day, when I’d accidentally release two dozen baby shrimp into the open water, sending the adult fish into a feeding frenzy. A classic case of good intentions gone wrong.
HeadtoHead: The RealWorld Showdown
Let’s get practical. Which one is right for your specific situation?
For a Heavily Stocked Tank
If you’re pushing the limits of your tank’s bioload (a common scenario in small tanks), you need all the filtration you can get. The winner here is the HOB filter. Its larger media capacity means more room for beneficial bacteria to colonize, which is crucial for processing ammonia and nitrite. That extra biological filtration is a safety net you’ll be glad to have.
For a Shrimp Tank
Shrimp are tiny and can easily get sucked into filter intakes. While a HOB with a prefilter sponge is perfectly safe, many shrimp keepers prefer a gentle internal filter with a sponge cover. The slow flow is less stressful for them, and the sponge itself becomes a secondary site for biofilm, which is a prime food source for shrimp. You can’t go wrong either way, but the internal has a slight edge for dedicated shrimp colonies.
For a Planted Tank
This is a tricky one. Plants love the CO2 that gets knocked out by a HOB’s waterfall, which is a negative. But they also benefit from the superior water circulation a HOB provides, distributing nutrients evenly. For a lowtech planted tank, a HOB is often fine. For a hightech, CO2injected tank where you’re fighting to keep CO2 levels high, a gentler internal or a canister filter is usually the better call to minimize surface agitation. The Fluval Plant Nano is a popular internal option that’s designed with planted tanks in mind.
For a Betta Tank
Bettas need calm water. Their long, flowing fins make them terrible swimmers in a strong current. Many HOBs are too powerful for a standard 5gallon betta tank, even on the lowest setting. In this case, a lowflow internal filter is often the perfect choice. You can even find tiny ones specifically marketed for betta bowls and nano tanks. Just be sure to baffle the output if it’s still too strong.
The Final Verdict: It’s About Your Priorities
After all this, you’re probably looking for a simple answer. Here it is.
For most small, general community tanks (think a 10gallon with some tetras and corydoras), a HangOnBack filter is my top recommendation. The combination of more media, easier maintenance, and better oxygenation is just too valuable, especially for a beginner. The space you save inside the tank is the clincher.
Choose an Internal Filter if your top priority is a clean external aesthetic, you’re keeping very lowflow fish like bettas, or you’re working with an extremely small tank (under 5 gallons) where even a small HOB would be overkill.
The biggest mistake I see people make is buying the cheapest option without considering these longterm factors. A filter isn’t just a water cleaner; it’s the life support system for your entire aquatic world. It’s worth a little extra thought and a few extra dollars.
For more detailed specifications and flow rates, checking the guides on sites like the Fishlore Aquarium Forum or the Aqueon product guides can be incredibly helpful before you buy.
Your Filter Questions, Answered
Can I use both a HOB and an internal filter in one tank?
Absolutely! This is a prolevel move, especially in a small tank. You can use the HOB for your main biological and chemical filtration and a small, spongebased internal filter just for extra mechanical filtration and water polishing. It’s also a fantastic way to “seed” a new tank with beneficial bacteria from an established one.
How often should I clean my small tank filter?
Don’t fall into the “out of sight, out of mind” trap. For a small tank, which is more sensitive to water parameter swings, check your filter media every 24 weeks. But here’s the critical part: never replace all the media at once, and never rinse it in tap water. The chlorine will kill your beneficial bacteria. Always rinse the sponges in a bucket of water you’ve removed from the tank during a water change.
Are sponge filters better than both HOBs and Internals?
Sponge filters are a third, excellent option, especially for breeding tanks and shrimp tanks. They are incredibly gentle, provide a huge surface area for bacteria, and are cheap and reliable. Their downside is they provide zero chemical filtration and are purely biological/mechanical. They also need an air pump to run, which can be noisy. They’re a fantastic tool, but not necessarily a direct replacement in every scenario.
What’s the next step?
Now that you’re armed with the realworld pros and cons, take a look at your tank. Look at the fish you have (or want to get). Think about your own tolerance for maintenance and noise. Your perfect filter choice is the one that fits your specific life and your tank’s unique needs.
Happy fish keeping!