Guide
Comparing different aquarium filters
The best filter depends on tank size, livestock, and maintenance style.
- HOB (hang-on-back) filters: Best all-rounder for tanks up to 200 L (55 gal). Easy to maintain, easy to find media for, and reliable enough for most community setups.
- Canister filters: The right choice for tanks over 200 L, heavily planted tanks, or any setup where flow and media volume actually matter. More expensive and slower to service, but the filtration capacity is genuinely better.
- Sponge filters: Underrated and underused. Ideal for breeding tanks, fry rearing, quarantine, and any fish that hates surface agitation - bettas, small rasboras, killifish.
- Internal filters: Fine for tanks under 60 L (15 gal), but they eat up interior space and most models top out at mediocre biological media capacity. Upgrade when your tank does.
- Turnover rate matters more than filter brand: Aim for 5-10× your tank volume per hour for most community fish. Understocking your filter is the single most common cause of unstable water quality.
- No filter type replaces the nitrogen cycle: Whatever you choose, it must complete a full cycle before you add fish. See how to cycle a fish tank if you're starting fresh.
Why filter choice actually matters
Most beginner guides treat filter selection like a minor detail. It isn't. The filter is the life-support system for your tank - it processes ammonia from fish waste, drives gas exchange at the surface, and houses the bacterial colonies that make the whole nitrogen cycle work. Choose one that's undersized, poorly suited to your fish, or awkward to maintain, and you'll be fighting water quality problems indefinitely.
There's no single best filter type. The right answer depends on your tank size, the species you keep, your maintenance habits, and your budget. What follows is a straightforward breakdown of each type - what it actually does well, where it falls short, and who it's genuinely for.
HOB (hang-on-back) filters
HOB filters clip onto the back rim of your tank, draw water up through an intake tube, pass it through a media chamber, and return it over a spillway. They're the default choice in most fish stores, and for good reason: they're cheap, widely available, simple to service, and they work.
What they do well
A decent HOB - brands like Aquaclear, Marineland Penguin, or Fluval C-series - gives you a generous media basket you can customise with sponge, biological media like ceramic rings or Matrix, and carbon or Purigen if needed. Servicing takes five minutes: pull the basket, rinse mechanical media in old tank water, replace chemical media on schedule, leave biological media alone. The spillway also provides solid surface agitation, which keeps dissolved oxygen levels up without needing a separate air pump in most cases.
For a 100-200 L (25-55 gal) community tank with tetras, livebearers, or corydoras, a quality HOB rated for your tank size will handle the biological load comfortably. These are genuinely good filters - not just a beginner stepping stone.
Where they fall short
HOBs have a few real limitations. The media chamber is smaller than a canister, so on a heavily stocked or large tank you're working harder to keep ammonia and nitrate in check. The waterfall return can also be noisy if your water level drops even a few centimetres - worth knowing if the tank is in a bedroom. And on tanks over 200 L, you often need two HOBs running in parallel to get adequate turnover, at which point a canister starts making more economic sense.
Most people replace the entire filter cartridge on schedule because the packaging tells them to. Don't. Those cartridges contain your biological media. Tossing them out every month crashes your cycle and spikes ammonia. Rinse mechanical media gently in old tank water; replace it only when it physically falls apart.
Canister filters
Canisters sit in your cabinet below the tank. Water is drawn down through an intake, passes through stacked media trays inside a sealed pressurised canister, then pumps back up to the tank via a spray bar or return nozzle. They're more complex than HOBs, but that complexity comes with real benefits.
What they do well
Media volume is the headline advantage. A mid-range canister like the Fluval 307, Eheim Classic 350, or Oase Biomaster holds significantly more biological and mechanical media than any HOB at the same price point. That extra capacity means a more stable nitrogen cycle, lower nitrate accumulation between water changes, and more headroom if you're stocking densely.
Canisters are also quieter than HOBs (the motor is submerged and enclosed), they leave the tank interior completely clear, and a spray bar return can be angled to create excellent mid-water flow without surface turbulence - useful for discus (Symphysodon spp.), blackwater setups, or CO2-injected planted tanks where you want to minimise outgassing.
Aim for your total tank volume to pass through the filter 5-10 times per hour. For messy fish like goldfish or cichlids, lean toward the higher end.
Where they fall short
Setup takes longer, priming can be fiddly the first time, and maintenance - usually every 6-8 weeks for mechanical media, less often for biological trays - means disassembling hose connections under your cabinet. None of this is hard, but it does take more time than a HOB. If you're the kind of keeper who delays maintenance, a canister will remind you by dropping flow rate noticeably when the mechanical sponges clog.
They're also overkill for small tanks. Running a large canister on a 60 L (15 gal) tank creates excessive flow, and you're paying for media capacity you don't need.
Canister filter marketing leans heavily on "rated for X litres" claims that assume a lightly stocked tank with regular water changes. If you're keeping messy fish - goldfish, oscars, large cichlids - buy a canister rated for at least 1.5× your actual tank volume, or double up.
Sponge filters
A sponge filter is exactly what it sounds like: a block of porous foam on a lift tube, driven by an air pump. Water is drawn through the sponge by the rising column of bubbles, mechanical debris gets trapped in the foam, and the enormous surface area colonised by beneficial bacteria handles biological filtration.
What they do well
Sponge filters are the right tool for several specific jobs, and nothing else comes close for those jobs. In a breeding or fry tank, the gentle, diffuse flow means newborn fry won't get sucked against an intake. In a quarantine tank, a pre-seeded sponge filter running in your main tank can be dropped straight into a hospital tank and provide instant biological filtration - no cycling delay when a fish gets sick. For fish that genuinely dislike current - bettas (Betta splendens), chocolate gouramis (Sphaerichthys osphromenoides), ember tetras - a sponge filter keeps the water clean without stressing the fish.
They're also cheap, nearly indestructible, and trivial to maintain: rinse the sponge in old tank water every few weeks, reassemble, done. Running costs are limited to the air pump electricity.
Where they fall short
Sponge filters don't move much water and have no mechanical separation between coarse and fine filtration. On a heavily stocked tank or one with large, messy fish, they'll clog quickly and won't keep up with the bioload. They also add visible equipment and tubing to the tank - not ideal for a display aquascape. And the constant bubbling noise bothers some people.
Keep a spare sponge filter running in your main tank at all times. When you need a quarantine tank in a hurry - and eventually you will - you'll have instantly cycled biological media ready to go. It costs almost nothing and takes up no meaningful space.
Internal filters
Internal filters are submersible units that mount inside the tank, usually via a suction cup. They're self-contained: impeller, media, and intake all in one housing. Most run off the mains; some smaller models are air-driven.
What they do well
For tanks under 60 L (15 gal) - small desktop aquariums, nano planted tanks, single betta setups - an internal filter is often the most practical option. It's compact, the whole unit costs less than a quality HOB, and setup is genuinely five minutes. Some models like the Fluval U-series offer decent media customisation for their size.
Where they fall short
Internal filters occupy tank space, which matters in a small aquarium. Media volume is limited, which limits biological capacity. Flow rates on most models are lower than a comparable HOB. As tanks get larger, the case for an internal filter weakens fast - by the time you're at 80-100 L, an HOB will outperform any internal filter at similar cost and keeps your tank interior cleaner.
Internal filters positioned poorly can create a dead zone in the opposite corner of the tank where waste accumulates and water becomes stagnant. Position the return nozzle to create a circular flow pattern that reaches the full tank volume - usually pointing toward the front glass at a slight upward angle.
How to actually choose
Filter selection comes down to four questions: How big is the tank? How densely stocked? What species? How much time do you want to spend on maintenance?
Under 60 L: Internal filter or sponge filter. If it's a betta or a shrimp tank, sponge. If it's a community nano, internal with a flow adjuster or a small HOB.
60-200 L: A quality HOB is the default answer. Match or slightly exceed the manufacturer's rated capacity for your tank volume. For a planted tank with CO2 where you want to minimise surface turbulence, consider a canister with a spray bar instead.
Over 200 L: Canister. Full stop. The media capacity and flow consistency justify the extra cost and maintenance time.
Breeding, fry, or quarantine tanks: Sponge filter, regardless of size.
Whatever you choose, understand what's actually happening inside it. The nitrogen cycle is entirely dependent on stable biological media - meaning consistent temperature, water chemistry, and flow. Disrupting any of these stalls your cycle and can spike ammonia fast. If you want to stay on top of those parameters without keeping a paper log, App-aquatic lets you track test results, set maintenance reminders, and flag when readings drift out of range.
Also think honestly about your stocking. An underpowered filter on an overstocked tank is a water quality problem waiting to happen. Run your planned stock list through the free stocking calculator before you buy - it'll tell you what bioload you're working with, which informs how much filtration you actually need. And remember that good filtration reduces but doesn't replace regular water changes; nitrate still accumulates regardless of how good your filter is.
Filter brand wars online are mostly noise. A mid-range Fluval, Eheim, or Aquaclear will outlast years of arguments about which is marginally better. What matters far more is whether the filter is correctly sized, whether you maintain it consistently, and whether your biological media stays undisturbed between services. A cheap filter maintained well beats an expensive one neglected for four months.
Track your parameters and get care reminders with App-aquatic.
Get the free appCan I run two different filter types on the same tank?
Yes, and it's often a good idea. A canister paired with a sponge filter, or two HOBs on a large tank, gives you redundancy - if one needs servicing or fails, the other maintains the cycle. It also distributes flow more evenly across the tank.
How do I know if my filter is too small for my tank?
The clearest signs are persistent ammonia or nitrite readings above zero, nitrate climbing rapidly between water changes, or visible waste settling on the substrate that the filter isn't picking up. Check your turnover rate - you want at least 5× tank volume per hour - and consider your actual stocking level, not just tank size. See aquarium water parameters for target ranges.
Do I need to run carbon in my filter?
Not as a permanent fixture. Carbon removes dissolved organics, certain medications, and odours, but it exhausts quickly (usually within 2-4 weeks) and takes up space that could hold more biological media. Use it after medicating a tank to clear the drug, or to polish water clarity temporarily. Otherwise, replace it with ceramic rings or a similar high-surface-area biological media.
Will a new filter work straight away, or does it need to cycle first?
All new filters need to cycle before they can handle a full fish load - this typically takes 4-6 weeks from scratch. You can speed it up by seeding the new filter with media from an established tank, or by running both filters simultaneously for 4-6 weeks during a transfer. Never replace an established filter with a new one overnight. Read the full process in how to cycle a fish tank.
How often should I clean my filter?
Mechanical media (coarse sponge, filter floss) needs rinsing every 2-4 weeks depending on stocking level - when flow visibly drops, it's overdue. Biological media should be rinsed gently in old tank water only when flow is genuinely restricted, and never replaced unless it's physically degraded. Cleaning too aggressively or too often is as harmful as not cleaning at all. Always rinse in water taken from the tank, never tap water.