Beginners Guide8 min readUpdated 30 August 2026
Aquarium Filter Guide: Which Filter to Buy for Your Tank
Five filter types, what each is actually good for, Indian prices, and how to size flow rate so you do not underfilter a tank or blast small fish across the glass.
The filter is the most important piece of equipment in an aquarium, and the one beginners most often size wrong. Its main job is not making water look clear. It is housing the bacteria colony that converts toxic ammonia into nitrite and then into far less harmful nitrate. Everything else is secondary.
The Three Jobs a Filter Does
- Mechanical: traps solid waste, uneaten food and debris in sponge or floss. This is the part you rinse.
- Biological: houses nitrifying bacteria on ceramic rings, bio balls or sponge. This is the part you must never wash under a tap.
- Chemical: activated carbon, resins or Purigen remove dissolved compounds, odours and medication residue. Optional, and carbon needs replacing monthly.
Filter Types Compared
| Type | Best for | Price (INR) | Pros | Cons |
|---|---|---|---|---|
| Sponge filter (air driven) | Betta tanks, fry, quarantine, shrimp, nano tanks | ₹150-₹600 | Cheap, gentle, superb biological media, cannot suck in fry | No mechanical polish, needs an air pump, visible in tank |
| Internal power filter | Tanks 1-3 feet, general community use | ₹400-₹1,500 | Cheap, easy, good flow, widely available in India | Takes up tank space, limited media volume |
| Hang on back (HOB) | Tanks 2-4 feet | ₹1,200-₹4,000 | Easy to service, keeps tank space free, good surface agitation | Noisy if water level drops, evaporation, needs back clearance |
| Canister filter | Tanks 3 feet and up, planted tanks, big fish | ₹3,500-₹18,000 | Huge media capacity, quiet, hidden in the cabinet, best biological load | Expensive, fiddly to prime and service |
| Sump filter | Tanks 5 feet+, arowana, marine, breeders | ₹8,000-₹40,000+ | Massive capacity, easy to add equipment, best for very large fish | Needs a drilled tank or overflow, complex, noisy if built badly |
How to Size a Filter
Look at the litres per hour (LPH) rating. The rule of thumb is 4 to 6 times your tank volume per hour for a normal community tank, and 6 to 10 times for heavily stocked tanks, goldfish, or large messy fish like Oscars and flowerhorns.
| Tank size | Approx volume | Community tank LPH | Heavy stocking LPH | Recommended type |
|---|---|---|---|---|
| 1 ft nano | 15-25 L | 100-150 | 150-250 | Sponge or small internal |
| 1.5 ft | 30-45 L | 150-250 | 250-400 | Internal power filter |
| 2 ft | 55-70 L | 250-400 | 400-700 | Internal or small HOB |
| 2.5 ft | 90-110 L | 400-600 | 600-1000 | HOB or small canister |
| 3 ft | 130-160 L | 600-900 | 900-1500 | HOB or canister |
| 4 ft | 200-250 L | 900-1400 | 1400-2200 | Canister |
| 5 ft+ | 350 L+ | 1500+ | 2500+ | Canister x2 or sump |
💡Manufacturer LPH ratings are measured with empty media and no head height. Real world flow is typically 30-40% lower. Buy one size up from what the chart says and you will never regret it.
Matching Filter to Fish
- Betta: gentle flow only. A sponge filter or an internal filter with the outlet baffled. Strong current exhausts a betta and shreds its fins.
- Goldfish and koi: massively overfilter. They produce more waste than any tropical fish. Aim for 8-10x turnover.
- Guppies, mollies, platies: standard internal or HOB is fine, but baffle the intake if fry are present.
- Discus: canister with high biological capacity plus frequent water changes. Discus are unforgiving about nitrate.
- Oscar, flowerhorn, arowana: canister or sump, sized generously. These fish are waste machines.
- Shrimp and fry tanks: sponge filter only, or a pre-filter sponge on any intake.
- Planted tanks: canister with a spray bar, moderate flow, no surface thrashing (it drives off CO2).
Filter Media: What Goes Inside
| Media | Job | Replace? | Price (INR) |
|---|---|---|---|
| Coarse sponge | Mechanical, first stage | Only when falling apart | ₹100-₹400 |
| Filter floss / wool | Fine mechanical polish | Every 3-4 weeks | ₹80-₹250 |
| Ceramic rings | Biological, high surface area | Almost never | ₹200-₹800/kg |
| Bio balls | Biological, high flow | Never | ₹200-₹600 |
| Activated carbon | Chemical, removes odour and medication | Monthly | ₹150-₹500 |
| Purigen | Chemical, removes organics, regenerable | Regenerate every few months | ₹800-₹1,800 |
How to Clean a Filter Without Killing the Cycle
- During your weekly water change, keep a bucket of the old tank water.
- Switch off the filter and open it.
- Squeeze and swirl sponges and rinse ceramic media in that bucket of tank water. Never under a tap.
- Replace filter floss if it is disintegrating. Do not replace every media type at once.
- Clean the impeller shaft and housing with a cotton bud. This is the most common cause of a filter losing flow.
- Reassemble, prime if needed, and restart.
Common Filter Mistakes
- Turning the filter off at night. The bacteria need constant oxygenated flow and start dying within an hour.
- Buying a filter rated for exactly your tank volume instead of 4-6 times it.
- Replacing all the media at once, which throws away the entire bacteria colony.
- Washing media under a chlorinated tap.
- Running a powerful filter in a betta or fry tank with no baffle.
- Ignoring the impeller until the filter stops. Ten minutes of cleaning a month prevents this.
- Relying on carbon as the main media. Carbon does nothing for ammonia.