Beginner Guide · Equipment

Aquarium Filter Types Explained

The filter is the most important piece of equipment in any aquarium — it's where your nitrogen cycle actually lives. This guide covers every common type, how to set up your filter media correctly, and how to maintain it without crashing your biology.

⚖ Biological Filtration 🔥 Chemical & Mechanical 🔬 Media Layering 🇿🇦 SA Hobby Focus
01

Three Types of Filtration

What Every Filter Must Do
1

Biological

The most critical — colonies of beneficial bacteria (Nitrosomonas and Nitrobacter) living in porous filter media that convert toxic ammonia → nitrite → nitrate. Without this, fish die. This is why you never fully replace all your filter media at once.

2

Mechanical

Physical removal of suspended particles — uneaten food, fish waste, plant debris — by passing water through sponge, floss, or mesh. Keeps the water visually clear and reduces the organic load on your biology.

3

Chemical

Activated carbon, Purigen, Zeolite, and similar media that absorb dissolved impurities (tannins, medications, chlorine, heavy metals). Optional in a well-maintained planted tank, but useful for emergencies and polishing water clarity.

The golden rule: All three types work together, but biological filtration is the only one that keeps fish alive. A filter that does brilliant mechanical filtration but has no suitable surface area for bacteria is still a dangerous filter.
02

Filter Types

Choose the Right Tool for Your Tank

Sponge Filter

The hobby workhorse — deceptively effective
Beginner Friendly Budget

A simple foam block through which an air pump draws water. Air-driven, inexpensive, and one of the most reliable biological filters available — the porous foam hosts enormous bacterial colonies. The go-to choice for shrimp tanks, breeding tanks, fry tanks, and quarantine setups where low flow and gentle water movement matter.

Best For

  • Shrimp and nano tanks where flow must be gentle
  • Fry and breeding tanks — no risk of sucking up baby fish
  • Quarantine tanks — easy to seed with existing media
  • As a supplement biological filter alongside another type

Pros

  • Excellent biological surface area — bacteria thrive in porous foam
  • Extremely cheap to buy and run — just needs a small air pump
  • Nearly indestructible with proper care
  • Easy to seed a new tank — transfer one sponge from a cycled tank

Cons

  • Limited mechanical filtration compared to multi-stage filters
  • Air pump noise can be noticeable in a quiet room
  • Not ideal as the sole filter for heavily stocked or large tanks
  • Aesthetic — visible in the tank, can look untidy in a display aquascape

Maintenance

  • Rinse in old tank water (never tap water) when flow noticeably drops
  • Never wring out or wash under the tap — this kills the bacteria colony
  • Monthly light squeeze in a bucket of tank water is all it needs
SA Tip: Sponge filters paired with a small USB or plug-in air pump are among the most affordable filtration setups available locally and are sold at most fish stores. Excellent first filter.

HOB / Power Filter

Hang-On-Back — versatile all-rounder
Easy Mid-Range Cost

Hangs on the back wall of the tank, drawing water up through an intake tube and passing it through filter media before returning it over a waterfall weir. The most common filter type for beginner and intermediate freshwater tanks between 60–300L. Handles all three filtration types in one compact unit.

Best For

  • Beginner community tanks from ~60L upward
  • Moderately stocked tanks where a canister would be overkill
  • Planted tanks — the surface agitation from the waterfall improves CO2 distribution on low-tech setups

Pros

  • Easy to set up and maintain — media is accessible without opening a sealed unit
  • Good mechanical and biological filtration in one
  • Self-primes on most models — easy restart after power cuts
  • Flow rate adjustment often built in

Cons

  • Surface agitation can drive off CO2 on pressurised planted tanks
  • Limited media volume compared to a canister of similar flow rate
  • Visible on the back of the tank — noticeable in display setups
  • Not ideal for tanks larger than ~300L as the sole filtration

Maintenance

  • Rinse mechanical media (floss/sponge) in old tank water monthly
  • Never replace all media at once — cycle it out over weeks
  • Check impeller for blockages if flow drops noticeably
Tip: On a CO2-injected planted tank, reduce the HOB flow rate so the waterfall barely breaks the surface — this significantly reduces CO2 off-gassing.

Canister Filter

External sealed unit — serious filtration power
Intermediate Higher Cost

A sealed canister that sits below the tank, drawing water down through inlet and outlet pipes. Water is forced through multiple layers of media under pressure, giving far more filtration capacity than any hang-on unit of the same footprint. The preferred choice for heavily planted tanks, cichlid tanks, large setups, and CO2 injected aquascapes.

Best For

  • Tanks over 150L, heavily planted, or heavily stocked
  • CO2 injected aquascapes — no surface agitation to drive off gas
  • African and South American cichlids with high bioloads
  • Anyone who wants maximum biological capacity

Pros

  • Largest biological surface area of any external filter type
  • Quiet — sits in a cabinet below the tank, out of sight
  • Multiple media baskets allow custom layering
  • No surface agitation — ideal for CO2 systems

Cons

  • More expensive upfront — quality brands (Fluval, Eheim, Oase) cost significantly more
  • Priming after maintenance can be fiddly on some models
  • If it leaks, it leaks below the tank — check hose connections regularly
  • Full maintenance is more involved than an HOB

Maintenance

  • Full clean every 3–6 months depending on bioload
  • Rinse mechanical media in old tank water; never replace biological media all at once
  • Check inlet/outlet pipes and spray bar for blockages regularly
SA Tip: Fluval, Eheim, and Oase canisters are all available locally. Second-hand units in good condition are common in club sales — a cleaned, serviced canister with new impeller is as good as new.

Internal Filter

Submersible unit — compact and quiet
Beginner Friendly Budget

A self-contained submersible filter that suction-cups to the inside of the tank wall. Mechanically and biologically functional for smaller tanks, and very quiet in operation. Most commonly used in tanks up to about 100L, quarantine tanks, and as supplementary circulation in larger setups.

Best For

  • Small tanks up to ~80–100L
  • Quarantine and hospital tanks
  • Additional circulation in a larger tank alongside a canister
  • Budget setups where HOB/canister cost is prohibitive

Pros

  • Inexpensive and widely available at all SA fish stores
  • Quiet and simple to operate
  • Easy to move between tanks for quarantine use
  • Self-primes on power-on — reliable after load-shedding

Cons

  • Visible inside the tank — aesthetically limiting in display setups
  • Limited media volume and biological capacity compared to canister or HOB
  • Flow rates often fixed or poorly adjustable
  • Not suitable as the sole filter for tanks over ~100L or cichlid/goldfish setups

Maintenance

  • Rinse foam cartridge in tank water every 2–4 weeks
  • Clear impeller and housing monthly
  • Replace cartridges gradually, not all at once
Tip: An internal filter seeded with media from an established tank is the fastest way to cycle a quarantine tank in a hurry — simply swap the media across.

Sump

Secondary tank below — maximum capacity
Advanced High Cost

A secondary tank below the display tank, connected by an overflow system and a return pump. Massively increases total water volume, allows a protein skimmer (for reef tanks), and can house a refugium with macroalgae or live plants for additional nutrient export. The gold standard for large reef aquariums and serious freshwater systems.

Best For

  • Reef and marine aquariums where a protein skimmer is required
  • Large heavily stocked freshwater systems over 400L
  • Advanced hobbyists who want complete control over water chemistry
  • Setups where all equipment must be completely hidden

Pros

  • Enormous biological and mechanical capacity
  • All equipment out of the display tank — cleanest aesthetic possible
  • Massive total water volume buffers chemistry swings
  • Refugium section can grow macroalgae for natural nutrient export

Cons

  • Requires a purpose-built cabinet and careful plumbing
  • Return pump failure can drain the display tank — float switch is essential
  • Significant cost and DIY/planning skill required
  • Not practical for rental accommodation or temporary setups

Maintenance

  • Clean mechanical sock/floss weekly in reef tanks
  • Trim refugium macroalgae regularly to export nutrients
  • Check all plumbing connections monthly for salt creep or leaks
Tip: A simple DIY sump using a second glass tank and a return pump is well within reach of an experienced hobbyist — several ECAAC members have built their own. Come to a meeting for advice before drilling your display tank.
03

How to Layer Your Media

Order Matters — Here's Why
1

Coarse Mechanical (First)

Large sponge or coarse foam pad. Traps big particles — fish waste, plant debris — before they reach biological media. Clean most frequently.

2

Fine Mechanical (Second)

Fine filter floss or a fine-grade sponge. Polishes the water before it reaches biological media, extending the time between biological cleans.

3

Biological Media (Third)

Ceramic rings, sintered glass, bio-balls, or bio-home. The home of your nitrogen cycle bacteria — maximum porous surface area. Disturb as little as possible and never replace all at once.

4

Chemical Media (Last, Optional)

Activated carbon, Purigen, or Zeolite. Sits last so clean water passes through it. Remove before medicating the tank — chemical media absorbs most medications.

Why this order? Water enters dirty and leaves clean. Coarse mechanical goes first so it traps big waste before it clogs the fine floss. Fine mechanical goes second to polish the water before it reaches the biology. Chemical media goes last so clean water passes through it — if it were first, it would clog almost immediately with physical waste.
The one rule that matters most: Never replace all your biological media in a single maintenance session. Even "rinsing" it under tap water kills the colony (chlorine and chloramine are fatal to bacteria). Always rinse bio-media gently in a bucket of old tank water removed during a water change. If you must replace bio-media, do it in stages — half now, half in 4 weeks — so the cycle never fully crashes.
04

Maintenance Frequency

A Quick Reference
Media TypeHow to CleanFrequencyReplace When?
Coarse foam / spongeSqueeze in old tank waterMonthly (or when flow drops)When it disintegrates — years
Fine filter flossDiscard and replaceEvery 2–4 weeksEvery clean — it's disposable
Ceramic rings / bio-mediaLight rinse in old tank water onlyEvery 3–6 monthsAlmost never — lasts years
Sintered glass (e.g. Ehfimech)Light rinse in old tank waterEvery 6 monthsEvery few years
Activated carbonCannot be cleaned — discardReplace every 4 weeksMonthly (loses effectiveness quickly)
PurigenRegenerate per manufacturer instructionsWhen discoloured (usually 4–8 weeks)After ~5 regenerations

Never Do a Full Filter Clean and a Large Water Change on the Same Day

Both at once removes too much biology and chemistry stability at the same time. Do your water change one week, and your filter maintenance the next, to keep the nitrogen cycle running smoothly between sessions.

05

Did You Know

Filter Curiosities

Flow Rate Isn't Everything

A filter rated at "10x tank volume per hour" with poor media choices can be outperformed by a smaller, well-set-up filter with excellent biological surface area. Media quality matters more than rated turnover.

A Mature Filter Is Priceless

A sponge or ceramic media from a tank that's been running 12 months is worth far more than any "bacterial starter" product — the colony is enormous, established, and proven to work in your specific conditions.

Bacteria Starve Without Ammonia

If you remove all fish for treatment or move a tank, the bacterial colony will begin to die off within days without an ammonia source. Dose ammonia or add a food source to keep the filter "fed" during any break.

Load Shedding Is a Real Risk

A filter that's been off for more than 4–6 hours can crash — not because the bacteria die immediately, but because anaerobic conditions in the media can produce hydrogen sulphide, which is toxic when flow resumes. Run the filter a few minutes before adding fish after a long outage.

Carbon Absorbs Medications

Activated carbon will absorb almost any medication you add to the tank — always remove it before starting any disease treatment, or the treatment will simply be filtered out before it can work.

"Mature" Filter Media Transfers Instantly

Moving established sponge, ceramic rings, or even gravel from a cycled tank into a new tank's filter can cycle the new tank in as little as 24–48 hours rather than 4–6 weeks — the fastest and most reliable way to start a new aquarium.

Questions About Your Filter Setup?

ECAAC members have experience with every filter type covered here. Come along to a meeting, bring photos, and get advice on whether your current setup is right for your tank and livestock.

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