Complete Aquarium Filter Guide: Choosing the Right Filtration System

A quality filter is the heart of any healthy aquarium. Proper filtration removes physical debris, breaks down toxic waste, and maintains the beneficial bacteria colonies that keep your fish alive.

This comprehensive guide covers every filtration type, helping you choose the perfect system for your specific tank and livestock.

Understanding the Three Types of Filtration

Mechanical Filtration:

Removes visible particles: uneaten food, fish waste, plant debris
Uses filter pads, sponges, or floss
Needs regular cleaning to prevent clogging
First line of defense

Chemical Filtration:

Removes dissolved pollutants: medications, tannins, odors
Uses activated carbon, Purigen, or specialized media
Optional for most established tanks
Useful for removing specific substances

Biological Filtration:

Most critical for fish health
Beneficial bacteria convert ammonia → nitrite → nitrate
Occurs on filter media, substrate, and decorations
Takes weeks to establish—never replace all at once

Filter Types Compared

1. Hang-On-Back (HOB) Filters

How They Work:

Hang on back rim of tank
Pull water up through intake tube
Pass through filter media cartridge
Return water via waterfall spillway

Best For:

Tanks 10-75 gallons
Beginners
Easy maintenance preference
Budget-conscious setups

Pros:

Affordable ($20-60)
Easy to install and maintain
Excellent surface agitation (oxygen exchange)
Good biological filtration capacity
Readily available replacement parts

Cons:

Visible equipment on tank rim
Limited media customization
Waterfall noise (some find soothing)
Can create strong currents
Filter cartridges expensive long-term

Recommended Models:

AquaClear: Best media capacity and customization
Marineland Penguin: Bio-wheel adds extra biological filtration
Fluval C Series: Multi-stage filtration
Seachem Tidal: High flow, self-priming, surface skimmer

Flow Rate Rule: Choose a filter rated for 1.5-2x your tank volume per hour. For a 40-gallon tank, select a filter rated for 60-80 GPH minimum.

2. Canister Filters

How They Work:

External canister sits below tank
Water drawn down through intake
Passes through multiple media baskets
Pumped back up to tank

Best For:

Tanks 40+ gallons
Planted tanks (gentle flow)
Heavy bioloads (cichlids, goldfish)
Customizable filtration needs
Quieter operation preference

Pros:

Massive media capacity
Fully customizable media
Powerful flow rates
Completely hidden (in cabinet or behind tank)
Very quiet operation
Excellent for large tanks

Cons:

Higher cost ($100-300+)
Complex initial setup
Requires maintenance every 3-6 months
Potential for leaks if not sealed properly
Overkill for small tanks

Recommended Models:

Fluval 07 Series: Reliable, efficient, easy maintenance
Eheim Classic: Legendary reliability, basic design
SunSun HW-302/304: Budget-friendly with good performance
Oase Biomaster: Premium with pre-filter and features

Setup Tips:

Place canister below water level for easy priming
Use quick-disconnect valves for maintenance
Layer media: mechanical → chemical → biological
Clean every 3-4 months (don’t overclean)

3. Sponge Filters

How They Work:

Air pump pushes air through uplift tube
Creates suction drawing water through sponge
Mechanical and biological filtration in sponge
Gentle bubbles return water

Best For:

Breeding tanks
Fry tanks (no suction danger)
Shrimp tanks
Hospital/quarantine tanks
Backup filtration
Tanks 5-40 gallons

Pros:

Extremely gentle filtration (no strong currents)
No danger to fry or small fish
Excellent biological filtration
Inexpensive ($10-30)
Never mechanical failure (no moving parts)
Easy to clean (squeeze in tank water)

Cons:

Requires air pump (additional purchase)
Bulky appearance in tank
No chemical filtration
Less mechanical filtration than other types
Takes up space inside tank

Recommended Models:

Hydro-Sponge Filter: High-quality, various sizes
Aquaneat Sponge Filter: Budget option, reliable
NYLON Bag Sponge: Can be hidden behind decor

Best Uses:

Primary filter for shrimp tanks
Secondary filter in heavily stocked tanks
Temporary filtration during filter maintenance
Breeding setups

4. Internal Filters

How They Work:

Submersible unit attaches inside tank
Draws water through intake grates
Passes through internal media
Returns water through outlet

Best For:

Nano tanks (5-20 gallons)
Tanks with no rim space for HOB
Supplemental filtration
Tanks requiring minimal equipment

Pros:

Compact and hidden inside tank
No external equipment
Often includes spray bar for gentle flow
Inexpensive ($15-40)
Good for aquascaped tanks

Cons:

Takes up space inside tank
Less powerful than external options
Harder to access for maintenance
Limited media capacity
Can be unsightly if not hidden

Recommended Models:

Aqueon QuietFlow Internal: Reliable, adjustable flow
Fluval U Series: Compact with good flow
Marina i25/i110: Nano tank specialists

5. Undergravel Filters

How They Work:

Plate sits under gravel substrate
Uplift tubes draw water down through gravel
Biological filtration occurs in gravel bed
Air pump or powerhead drives flow

Best For:

Bare tanks with simple gravel
Breeding setups
Tanks without plants
Very basic setups

Pros:

Completely hidden
Excellent biological filtration
No mechanical parts to fail
Very inexpensive

Cons:

Outdated technology
Traps debris in gravel (requires deep cleaning)
Incompatible with planted tanks
Limited mechanical filtration
Hard to clean effectively

Verdict: Generally not recommended for modern aquascapes.

6. Wet/Dry (Trickle) Filters

How They Work:

Water trickles over biological media
Maximum oxygen exposure
Extremely efficient biological filtration
Usually for sumps under tank

Best For:

Large tanks (75+ gallons)
Heavy bioloads (goldfish, cichlids)
Marine/saltwater systems
Dedicated fish rooms

Pros:

Ultimate biological filtration
Massive media capacity
Excellent oxygenation
Space for equipment in sump

Cons:

Complex setup
Requires drilling or hang-on-tank overflow
Large footprint
Overkill for most freshwater tanks
Expensive ($200+)

Verdict: Best for advanced hobbyists with large tanks.

Matching Filter to Tank Type

Nano Tanks (5-10 gallons):

Sponge filter with air pump
Small internal filter
Hang-on-back rated for 10-20 gallons

Community Tanks (20-40 gallons):

Hang-on-back filter (AquaClear, Tidal)
Small canister for planted setups
Sponge filter as supplement

Planted Tanks:

Canister with spray bar (gentle flow)
HOB with reduced flow
Avoid strong currents

Cichlid/Goldfish Tanks (Heavy Bioload):

Large canister filter
Multiple HOB filters
Consider wet/dry for 75+ gallons

Breeding/Fry Tanks:

Sponge filter (essential for safety)
Small air-driven box filter

Flow Rate Guidelines

General Rule: Filter should process 4-6x tank volume per hour

Examples:

20-gallon tank: 80-120 GPH filter
40-gallon tank: 160-240 GPH filter
75-gallon tank: 300-450 GPH filter

Adjust Based On:

Stocking level: Heavy stock needs higher flow
Fish preferences: Bettas need gentle flow
Plant density: Dense planting reduces flow needs
Surface agitation: More needed in warm water or with many fish

Filter Media Guide

Mechanical Media (Order Matters):

Coarse sponge/pad: Captures large debris first
Fine filter floss: Polishes water (last mechanical stage)

Biological Media:

Ceramic rings: Massive surface area for bacteria
Bio-balls: Good for wet/dry filters
Lava rock: Natural, porous, inexpensive
Filter sponge: Dual purpose (mechanical + biological)

Chemical Media (When Needed):

Activated carbon: Removes medications, tannins, odors
Purigen: Removes nitrogenous waste, polishes water
Phosphate remover: Controls algae

Pro Tip: Never replace all biological media at once. Rinse in tank water during water changes to preserve bacteria.

Installation and Setup

HOB Filter Setup:

Rinse filter media in tank water
Prime filter (fill with water before starting)
Adjust flow if needed
Check for proper waterfall flow
Monitor for leaks first 24 hours

Canister Filter Setup:

Place canister below tank level
Install intake and return hoses
Fill canister with media (mechanical → chemical → biological)
Prime according to manufacturer instructions
Check all seals before plugging in
Run and check for leaks

Sponge Filter Setup:

Attach to air pump with airline tubing
Place in tank where flow reaches all areas
Add check valve to prevent back-siphoning
Adjust air flow for desired filtration strength

Maintenance Schedule

Weekly:

Rinse mechanical media in tank water (if clogged)
Remove debris from intake strainer
Check flow rate hasn’t decreased significantly

Monthly:

Rinse or replace mechanical media
Clean impeller and housing
Check for unusual noise or vibration
Test flow rate

Quarterly (Canisters):

Disassemble and clean all parts
Replace worn seals
Deep clean media baskets
Never clean biological media with tap water

Annually:

Replace impeller if worn
Check all seals and gaskets
Deep clean canister motor housing
Consider replacing filter floss/carbon

Troubleshooting Common Filter Problems

Reduced Flow:

Check for clogged intake strainer
Clean mechanical media
Check for kinked hoses (canister)
Clean impeller and housing
Check for air locks (canister)

Noise Issues:

Ensure filter is level
Check impeller for debris or damage
Verify water level covers intake (HOB)
Lubricate seals with silicone grease
Check for air in canister

Water Cloudiness:

Mechanical media needs cleaning/replacement
Check if filter is properly sized for tank
May need additional filtration
Ensure adequate biological filtration

Frequent Clogging:

You’re overfeeding (reduce food)
Tank is overstocked
Mechanical media needs upgrade
Consider pre-filter sponge on intake

Multiple Filter Strategy

Many experienced aquarists run two filters:

Benefits:

Backup if one fails
Can clean one while other maintains bacteria
Increased total flow and capacity
Flexibility to run different media types

Combinations:

HOB + Sponge: Great for community tanks
Canister + HOB: Excellent for large/heavy stock
Two HOBs: Budget-friendly redundancy

Budget Recommendations

Under $30:

Sponge filter with air pump
Small HOB for nano tanks
Internal filter

$30-75:

Quality HOB (AquaClear, Tidal)
Budget canister (SunSun)

$75-150:

Premium HOB with features
Mid-range canister (Fluval 107)

$150+:

High-end canister (Oase, Fluval)
Wet/dry systems
Multiple filter setups

Conclusion

The right filter depends on your tank size, stocking, plants, and personal preferences. For most beginners, a quality hang-on-back filter like the AquaClear or Seachem Tidal offers the best balance of performance, ease of use, and value.

Remember: A filter is a life support system. Invest in quality, maintain it regularly, and never turn it off for more than a few minutes. Your fish depend on that constant water circulation and biological filtration.

Need help with water quality? Read our water parameter guide to understand what your filter should achieve.