Why Filtration Is Critical in Nano Tanks
In a large aquarium of 200 liters, a malfunctioning filter that stops running for 12 hours is inconvenient but rarely immediately lethal — the large water volume buffers ammonia accumulation long enough for the keeper to notice and respond. In a 10-liter nano tank, a filter failure for even 6-8 hours can produce ammonia levels toxic to fish, particularly in Cambodia's warm temperatures where bacterial decomposition of waste accelerates. Understanding and selecting the right filter is therefore proportionally more critical for nano tanks than for large community aquariums.
The three primary filter types suitable for nano tanks are sponge filters, small internal filters, and hang-on-back (HOB) filters. Each has distinct advantages and disadvantages relating to flow rate, biological filtration capacity, noise, maintenance accessibility, and safety for small fish and shrimp. The best filter for a specific nano tank depends on what is living in it, how the tank is positioned, and the keeper's maintenance preferences and budget.
All three filter types provide biological filtration through colonization of beneficial bacteria on their filter media surfaces — the primary mechanism for converting ammonia to nitrite and then nitrate. The larger the surface area of the filter media, the greater the biological filtration capacity. Sponge filters have excellent biological filtration due to the porous sponge surface; HOB filters with ceramic rings or bio-balls in the media chamber also provide excellent biological filtration; small internal filters typically have the smallest media volume and therefore the least biological filtration capacity for their physical size.
- ✦Never clean all filter media at once — always rinse in old tank water only, and clean only half the media per maintenance session
- ✦If a filter stops running, perform a 30% water change immediately and restart the filter as soon as possible
- ✦Keep a backup air pump and sponge filter in reserve — they cost very little and provide critical insurance against filter failure
Sponge Filters — The Best Choice for Shrimp and Fry
Sponge filters consist of a porous foam block mounted over a hollow uplift tube, powered by an air pump. Water is drawn through the sponge by the rising air bubbles, and bacteria colonize the sponge surface to perform biological filtration. The flow rate is very gentle and the intake is completely covered by the sponge, making it physically impossible for shrimp, baby shrimp, or small fry to be sucked into the filter and killed. This safety advantage makes sponge filters the unconditional best choice for shrimp colonies and breeding tanks.
Sponge filters are inexpensive, widely available at Cambodian aquarium shops, and extremely durable — a quality sponge filter can last 5-10 years with simple maintenance. The air pump that powers the sponge filter does produce some noise from the bubbling, but selecting a quality quiet air pump (brands like Atman, Jebo, or Sera available in Cambodia) and adjusting the air flow to the minimum needed for adequate circulation reduces noise to an acceptable level for most environments. The air pump can also run two sponge filters simultaneously using a Y-splitter, doubling filtration capacity.
The main limitation of sponge filters is aesthetic — the bulky sponge and airline tubing are not invisible within the tank and can disrupt the visual composition of a carefully aquascaped nano layout. Some hobbyists hide the sponge filter behind a cluster of plants or rocks, which works acceptably. For a nano tank where appearance is secondary to fish health and breeding success — such as a shrimp breeding tank — the sponge filter is without question the optimal choice.
- ✦Sponge filters are the only completely safe filter for baby shrimp — other filter types can and do kill them
- ✦Squeeze the sponge in old tank water (never tap water) every 4-6 weeks to remove accumulated waste without killing the beneficial bacteria
- ✦Two small sponge filters are better than one large one — they provide redundancy if one fails
Internal Filters — Compact and Versatile
Small submersible internal filters, the type that mounts to the inside glass wall of the tank via suction cups, are the most common filter type sold for nano tanks in Cambodia. Brands like Atman, Resun, Jebo, and Sobo produce models rated for 20-100 liter tanks that fit physically in a 10-15 liter nano tank and provide adjustable flow rates. The intake of most internal filters can be covered with a fine mesh pre-filter sleeve, available at aquarium shops for 2,000-4,000 KHR, to prevent small fish and shrimp from being drawn in.
Internal filters for nano tanks should be selected on the basis of minimum flow rate, not maximum — the lowest-rated models produce sufficient circulation for a 15-liter tank while minimizing the current that stresses small fish. Look for internal filters with an adjustable flow dial that allows flow reduction to 30-50% of maximum output. Filters without flow adjustment cannot be slowed and will create excessive current in small tanks, exhausting fish that must constantly swim against the flow.
Maintenance of internal filters involves monthly removal, rinsing of the sponge media in old tank water, and occasional cleaning of the impeller to remove debris that reduces flow. Most internal filters come apart with a simple twist mechanism and reassemble in minutes. The combination of biological filtration on the sponge and mechanical filtration through the sponge material makes internal filters a practical, complete solution for most nano tank applications where shrimp safety is not the primary concern.
- ✦Cover internal filter intakes with pre-filter sponge sleeves if housing fish smaller than 2 cm or any shrimp
- ✦Clean the impeller with a cotton swab every 2-3 months — a dirty impeller reduces flow by 30-50%
- ✦Choose the lowest-wattage model that meets your tank's needs — smaller motors run quieter and use less electricity
HOB Filters — Best Biological Filtration for Nano Tanks
Hang-on-back filters, which clip onto the rim of the tank with the filter chamber hanging outside the aquarium, provide the best biological filtration capacity of any filter type for their size because the external media chamber can be packed with ceramic rings or bio-balls offering enormous bacterial colonization surface area. For a nano tank of 15-20 liters requiring maximum water quality for sensitive species, a HOB filter rated for 40-60 liters at reduced flow provides superior biological filtration with good maintenance access.
The most important modification for using a HOB filter on a nano tank is reducing the intake flow to prevent the powerful suction from stressing or injuring small fish. This is achieved by covering the intake strainer with a pre-filter sponge, which also acts as a mechanical pre-filter to reduce the frequency of media cleaning. HOB filters sold in Cambodia by Atman and similar brands typically have intakes that accept standard pre-filter sponges as an add-on accessory.
HOB filters do produce a characteristic trickle sound as filtered water returns to the tank over the output lip — acceptable for most environments but potentially disruptive in very quiet study spaces. Raising the water level until the output is submerged eliminates the trickle sound entirely while maintaining filtration effectiveness. This simple adjustment makes HOB filters viable even in quiet environments. The media chamber in HOB filters is typically easier to access and clean than internal filters, as it sits entirely outside the tank.
- ✦Always use a pre-filter sponge on the HOB intake for any nano tank housing shrimp or fish under 3 cm
- ✦Raise the water level to submerge the HOB output spout — eliminates trickle noise completely
- ✦HOB filters dry out and need priming if the water level drops below the intake — top up the tank before this happens
Flow Rate Math: 3-5x Rule for Nano Tanks
The standard recommendation for aquarium filtration is that the filter should turn over the tank volume 3-5 times per hour at minimum, and up to 10 times per hour for heavily stocked tanks. For a 15-liter nano tank, this means a filter with an effective flow rate of 45-75 liters per hour for a moderately stocked setup, or up to 150 liters per hour for a heavily stocked tank. However, the rated flow on the box is always the maximum — actual flow after adding media is typically 60-70% of the rated maximum.
Apply the 3-5x rule to select the correct filter size, then adjust the flow rate down to the minimum that maintains good circulation and surface agitation. A gentle ripple on the water surface indicates adequate oxygen exchange — a violent surface churn is excessive for most nano fish species. Chili Rasboras and Sparkling Gouramis particularly dislike strong current, while Endlers and Ember Tetras are more tolerant of moderate flow. Matching the filter flow to the species needs prevents chronic stress even in a properly sized tank.
Cambodia-available brands for nano tank filters in the 50-150 liter per hour flow range include Atman, Jebo, Resun, and Sobo, all Chinese-manufactured brands sold at Phnom Penh aquarium shops at prices ranging from 15,000-60,000 KHR. While these brands do not match the build quality of premium international brands like Eheim or Fluval, they provide reliable service for nano tanks with regular maintenance and are the practical choice for most Cambodian hobbyists based on local availability and price.
- ✦For Chili Rasboras or Sparkling Gouramis, use the lower end of the 3x flow rate range — these species dislike strong current
- ✦Atman and Jebo filters are widely available in Phnom Penh and provide reliable performance for the price
- ✦If your fish are constantly swimming into the current without resting, the flow rate is too high — reduce it immediately