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Picking a filter for a nano aquarium feels small only until you see how fast water quality can swing. In a compact tank, waste builds up faster, oxygen drops quicker, and fish or shrimp have less room to escape strong flow. The right filter keeps water clear, stable, and safe. The wrong one causes noise, stress, and constant work. This guide shows you how to choose with confidence, step by step.
Introduction
Nano aquariums are usually 2 to 20 gallons. They are popular because they fit on desks and shelves and look clean and modern. They also demand thoughtful gear, and the filter is the most important part. A good nano filter is quiet, safe for small animals, easy to maintain, and strong enough to support the biofilter without blasting your livestock.
Read on to learn what a filter must do, how to match types to your plan, how to calculate flow, what media to use, and how to maintain everything with minimal fuss. You will see clear recommendations for bettas, shrimp, and small community fish. You will also get a simple checklist to make sure you do not miss anything.
What Nano Really Means and Why Filter Choice Matters
The word nano covers many sizes. Most hobbyists use it for tanks from 2 to 20 gallons. At this scale, the filter has to stabilize water quickly after every feeding and every small mistake. You cannot rely on volume to dilute problems. Filtration and maintenance do the heavy lifting.
Smaller tanks also magnify flow patterns. A filter that is mild in a 40 gallon can feel like a river in a 5 gallon. The best nano filter gives you adjustable flow and good media space. You want control, not brute force.
Know the Three Jobs of a Filter
Mechanical filtration
Mechanical filtration traps particles such as uneaten food, plant bits, and fish waste. Sponges and floss do this job. The goal is to remove debris before it decays and releases ammonia. In nano tanks, use a sponge with pores that match your load. Coarse foam resists clogging. Fine floss catches micro debris but needs more frequent rinsing.
Biological filtration
Biological filtration converts toxic ammonia to nitrite and then to nitrate. This process is done by beneficial bacteria that live on filter media, sponges, and all wet surfaces. In tiny tanks, stable biological filtration is non negotiable. You get stability by providing lots of surface area and by cleaning media gently so bacteria are not stripped away.
Chemical filtration
Chemical filtration uses adsorbents such as carbon or resins to remove dissolved organics, medications, or specific contaminants. It is optional and situational. Do not depend on it for basic water quality. Mechanical and biological filtration do the daily work. Use chemical media only when you have a clear goal.
The Main Filter Types for Nano Tanks
Sponge filters
Sponge filters are powered by an air pump. Air lifts water through foam, giving gentle mechanical and biological filtration with strong oxygenation. They are simple, cheap, and safe for shrimp and fry. They never leak, and they are easy to clean.
The downsides are the need for an air pump and airline management, plus visible bubbles and equipment in the tank. Air pumps can hum if not isolated. In very small displays, a sponge can look bulky. Performance depends on foam size and air rate, not on an impeller.
Hang on back filters
Hang on back filters sit on the rim and hang outside the glass. They draw water up a tube, pass it through media, and return it as a waterfall or spillway. They offer good media access, adjustable flow on many models, and they free up space inside the tank. They can run quietly if set up well.
Watch two things. First, protect the intake with a prefilter sponge if you keep shrimp or fry. Second, prevent splashing noise by keeping the water level high and keeping the filter box filled. Some small units push water too fast with limited space for media, so choose one with room to customize the media basket.
Internal power filters
Internal filters sit inside the tank and use a small pump to push water through a chamber of sponge and media. They can be very quiet because the pump is underwater. Some include a spray bar or directional nozzle, useful in nano layouts. Maintenance is simple if the housing opens easily.
They take up display space, and the body can add a little heat. You still need an intake guard for shrimp. Choose a model with a real media chamber, not only a thin cartridge.
Mini canister filters
Mini canisters sit below or next to the tank and move water through external hoses into a sealed canister with media trays. They give the most media capacity and flexible flow options with spray bars or pipes. They also keep the tank interior clean.
They require careful priming and hose management. There is a small risk of leaks if seals fail. Maintenance takes longer than a sponge or hang on back. In exchange, you get strong biological filtration in a compact footprint outside the tank.
Matten and corner filters
A matten filter is a large sheet of foam placed across one side of the tank with a lift behind it. Water moves evenly through the whole foam face. This gives enormous surface area, gentle flow, and superb safety for shrimp and fry. Corner filters are smaller versions that sit in a corner with a foam block and an air lift.
The tradeoff is space. You give up a slice of the tank to the foam wall. In return, you get low maintenance and very stable biofiltration. These are favorites for breeding and shrimp tanks.
All in one compartments
Some nano tanks include a rear filtration compartment. Water moves over a surface weir into chambers with sponge and media, then returns via a pump. These are tidy and reduce equipment clutter. Their weakness is limited media volume in very small models. Many benefit from media upgrades and intake guards at the overflow if you keep shrimp.
Match Filter to Your Stock and Goals
For a betta in 5 to 10 gallons
Bettas prefer calm water with stable warmth and lots of surface access. A low flow sponge filter or a small hang on back with adjustable flow and a baffle is best, with a turnover of 3 to 5 times per hour. Use a spray bar or baffle to diffuse the return. Keep the water level high to prevent waterfalls. Aim for gentle circulation around plants without pushing the fish.
For a shrimp colony in 5 to 15 gallons
Shrimp need oxygen, safe intakes, and mature biofilm. A sponge filter, matten filter, or internal filter with fine foam works well. Add a prefilter sponge to any intake. For growth and molting, keep flow broad and gentle. As a baseline, aim for 6 to 10 times of gentle distributed flow, not a single jet. Stable, oxygen rich water helps baby shrimp survive.
For a small community in 10 to 20 gallons
Small rasboras, tetras, and similar fish like steady, clean water with moderate movement. A hang on back or mini canister offers enough media and adjustable flow. Set a spray bar or wide spillway to spread current. Target 5 to 8 times per hour. If fish hug the bottom or struggle near the return, reduce flow or add plants and hardscape to break it up.
For a planted nano with added carbon dioxide
Plants generate oxygen by day and consume it at night. If you inject carbon dioxide, hold surface agitation moderate to retain gas while keeping oxygen adequate. Choose filters with good media space and a spray bar you can angle just below the surface. Keep biological media generous so the tank stays stable even with heavy plant biomass.
For a minimal equipment look
Pick an internal filter with a compact body, or a mini canister with glass or black pipes to match the background. Hide intakes behind plants or hardscape. A matten filter can also blend in if you match foam color to the background and place moss along the face.
Calculate the Right Flow
Filter boxes list flow as gallons per hour or liters per hour. Those numbers are measured with no media and no head height. Real flow is lower. In nano tanks, you want enough turnover to feed oxygen to bacteria and carry debris to the media without blasting fish.
As a baseline, aim for 5 to 8 times tank volume per hour for small community fish, 3 to 5 times for a betta, and 6 to 10 times of gentle distributed flow for shrimp. If you run fine floss or tall head height, select a filter rated about 1.5 times your target to account for real world reduction. Always favor adjustable flow and ways to spread return such as a spray bar or baffle.
Example targets. For a 5 gallon with a betta, aim for 15 to 25 gallons per hour after media. For a 10 gallon community, aim for 50 to 80 gallons per hour after media. For a 20 gallon, aim for 100 to 160 gallons per hour after media. If your filter is hard to adjust, use a prefilter sponge and a spray bar to soften and spread the flow.
Media Matters More Than Cartridges
Skip single use cartridges
Cartridges are convenient but wasteful and often weak in surface area. Replacing them often throws away bacteria and can crash the cycle. In nano tanks, that risk is big. Build your own media stack instead.
Build a simple, effective media stack
Use a coarse sponge for mechanical filtration, a generous amount of porous biological media, and only add carbon or resins when you have a specific reason. Place sponge or floss first to catch debris, then bio media in a bag or tray, and leave room for optional chemical media last. This layout works in hang on back, internal, and mini canister filters.
Size and pore structure matter
Choose foam that fits snugly and does not let water bypass. For bio media, ceramics, sintered glass, and lava rock all work if water can pass through them at a steady rate. Pack them loosely so flow is even. The goal is slow, steady contact, not a tight plug.
Noise, Vibration, and Aesthetics
A quiet nano setup is a joy to live with. Hang on back units can buzz if the impeller is dirty or if the water level is low and the spillway splashes. Keep the tank filled to the bottom of the spillway and seat the impeller well after cleaning. Internal filters are quiet but transmit vibration if pressed against glass. Center them and add a soft pad behind the mount if needed.
Air pumps can hum. Place them on a soft pad, not a hard surface. Use a check valve and a short, direct airline. If you hear gurgling, adjust the air rate or lift height on sponge filters so bubbles move smoothly.
Safety and Flow Management for Tiny Livestock
Small fish, shrimp, and fry can be injured by suction or fast jets. Add a prefilter sponge to every intake on nano tanks. This prevents clogging of the main media, protects tiny animals, and adds bonus biofiltration. Use a spray bar or a return nozzle pointed at the glass to spread out current. Baffle hang on back returns with a piece of sponge or a clip on guard if needed.
Keep an eye on dead spots. In tanks with dense planting or complex hardscape, add a small secondary flow source such as an air stone near the bottom to keep water moving gently through all zones. This prevents mulm piles and improves oxygenation without stressing fish.
Maintenance That Protects the Cycle
Plan a light but regular routine. Rinse sponges and floss in old tank water during a water change. Tap water can harm bacteria. Clean until flow returns, not until it looks brand new. Swish biological media gently only when flow drops through it. Vacuum debris from the substrate so it does not rot in place.
Rinse sponges and floss in old tank water every 1 to 2 weeks, swish biological media gently when flow drops, and never replace all media at once. If you run carbon for medication removal or odor, replace it every few weeks or remove it after the job is done. Prime canister filters carefully after maintenance and check seals.
Energy Use and Heat
Nano tanks lose and gain heat quickly. Internal power filters and pumps transfer some warmth into the water. In warm rooms this can tip the tank a degree or two. Choose low wattage equipment and monitor temperature during early days. If energy use matters, air driven sponge filters are often the most efficient per gallon filtered.
Step by Step Selection Checklist
Step 1. Define tank size and stock
Write down the exact volume and your planned animals. Betta, shrimp colony, or a small school of fish each have different flow needs and safety concerns.
Step 2. Choose a filter type that fits the goal
For bettas, pick a sponge or a gentle hang on back. For shrimp, choose a sponge, matten, or safe internal. For a community tank, use a hang on back or mini canister with adjustable return. For minimal gear inside the tank, pick a mini canister or a neat internal.
Step 3. Calculate your target flow
Use the turnover guidelines for your stock. Multiply tank volume by the range that fits your animals. Then select a filter rated about 1.5 times higher to cover real world losses. Make sure you have a way to reduce and spread flow.
Step 4. Plan your media
Use coarse foam first, lots of bio media second, optional chemical media last. Avoid disposable cartridges when possible. Add a prefilter sponge to every intake.
Step 5. Check noise, access, and aesthetics
Will you hear it from your desk or bed. Can you remove and rinse media without a mess. Does the equipment fit the look you want. Pick the option that you will maintain on schedule.
Step 6. Confirm safety for small animals
Install intake guards, fine foam where needed, and a spray bar or baffle. Test flow with a bit of food to see where it travels. Adjust until circulation is even and gentle.
Example Setups
5 gallon betta with plants
Use a medium pore sponge filter or a small hang on back with the return baffled. Target 3 to 5 times turnover. Fill the tank to reduce spillway noise. Add floating plants to diffuse the surface and give cover. Keep the prefilter sponge on the intake even if you think it is not needed. It slows flow and protects fins.
10 gallon shrimp colony
Use a double sponge filter or a matten filter. Target 6 to 10 times gentle flow. Add an extra small air stone near the substrate to prevent dead spots under moss or wood. Place leaf litter or cholla for biofilm growth. Keep fine prefilters clean so they do not clog and stall circulation.
20 gallon nano community
Use a hang on back or mini canister with a spray bar running the length of the back wall. Target 5 to 8 times turnover. Angle the bar slightly up to ripple the surface without splashing. Fill the media basket with coarse sponge and bio media. Vacuum substrate weekly to keep mechanical load light.
Troubleshooting Common Filter Problems
Reduced flow after a few days
Check for clogged prefilter sponges and fine floss. Rinse them in old tank water. If the impeller area is dirty, remove the rotor and clean the well with a small brush. For air driven sponges, verify the air stone is not clogged and the lift tube is clear.
Noisy rattle or buzz
Seat the impeller firmly and ensure the shaft and bushings are present. Raise the water level to stop waterfall noise. Place air pumps on a soft pad. Verify that hoses are not vibrating against the stand.
Microbubbles in the tank
Bubbles can come from a loose intake, low water in a hang on back, or a canister sucking air at a seal. Fill the filter box, reseat gaskets, and purge trapped air by tilting the unit under water. For a sponge filter, reduce air rate until bubbles form a steady stream.
Livestock pinned to the intake
Add or upgrade the prefilter sponge and reduce flow. Disperse return with a spray bar or by pointing the nozzle at glass. For shrimp, move to finer foam and broaden the flow path.
Budget and Upgrade Path
Start simple and scalable. A sponge filter is inexpensive, reliable, and excellent for biological filtration. If you add more fish later, you can keep the sponge as a secondary biofilter and add a hang on back or mini canister for higher mechanical capacity. Choose gear with swappable media trays so you can tune performance as the tank matures.
Putting It All Together
Filter choice is not about the biggest number on a box. It is about a balance of media capacity, adjustable and gentle flow, safety, noise, and ease of maintenance. In nano tanks, that balance keeps fish and shrimp calm and healthy while you enjoy clear water and low effort care. Decide your stock, pick a type that fits, calculate realistic flow, build a reusable media stack, and maintain lightly but regularly.
Conclusion
The best filter for your nano aquarium is the one that delivers steady biological filtration, captures debris before it decays, and moves water gently and evenly through the whole tank. For bettas, choose low flow with a baffle. For shrimp, choose foam based safety and broad circulation. For small communities, choose adjustable flow and decent media space. Keep media reusable and maintenance simple. Make these choices once, and your nano tank will stay stable, quiet, and clear.
FAQ
Q: What filter type is best for a 5 to 10 gallon betta tank
A: A low flow sponge filter or a small hang on back with adjustable flow and a baffle is best, with a turnover of 3 to 5 times per hour.
Q: How much flow does a nano tank need
A: As a baseline, aim for 5 to 8 times tank volume per hour for small community fish, 3 to 5 times for a betta, and 6 to 10 times of gentle distributed flow for shrimp.
Q: Which media should I use in a nano filter
A: Use a coarse sponge for mechanical filtration, a generous amount of porous biological media, and only add carbon or resins when you have a specific reason.
Q: How do I make my filter safe for shrimp and fry
A: Add a prefilter sponge to the intake, use a spray bar or baffle to spread out flow, and choose fine foam in the filter so tiny animals cannot be pulled in.
Q: How often should I clean a nano filter
A: Rinse sponges and floss in old tank water every 1 to 2 weeks, swish biological media gently when flow drops, and never replace all media at once.