The Three Jobs of an Aquarium Filter
Every aquarium filter performs three types of filtration: mechanical (removing solid waste particles), biological (beneficial bacteria converting ammonia and nitrite), and chemical (removing dissolved contaminants with activated carbon or other media). Understanding all three helps you choose the right filter and maintain it correctly.
Mechanical filtration uses foam pads, filter floss, or fine mesh to trap uneaten food, fish waste, and plant debris before they decay and release ammonia. This must be rinsed regularly — a clogged mechanical stage reduces water flow and forces harmful bacteria to grow in the clogged material.
Biological filtration is the most critical. Beneficial bacteria (Nitrosomonas and Nitrobacter) live on rough surfaces inside your filter — ceramic rings, bio-balls, lava rock, or K1 media. This stage must never be washed in tap water, which contains chlorine that kills the bacteria. Always rinse biological media in old tank water only.
Sponge Filters: Best for Small Tanks and Fry
Sponge filters are the simplest, most affordable, and most reliable filters available. They work by running an air pump through a foam sponge — beneficial bacteria colonize the sponge, and the bubbles draw water through it for filtration. A quality sponge filter for a 40-liter betta tank costs under $5 in Cambodia.
Sponge filters are ideal for: betta tanks, shrimp tanks, quarantine tanks, fry tanks (newborn fish cannot be sucked into a sponge filter), and hospital tanks. Their gentle flow suits fish that prefer low current, like bettas, guppies, and fancy goldfish.
The main limitation of sponge filters is flow rate — they cannot handle high bioloads. A 60-liter tank with 10 fish needs more filtration than a single sponge filter can provide. In these cases, use two sponge filters or pair a sponge filter with a secondary filter.
- ✦Run two sponge filters instead of one — same cost, double redundancy if one fails
- ✦Squeeze sponge in old tank water monthly — do not wring dry, just squeeze until clean
- ✦Bigger sponge = more bacteria = more biological capacity — bigger is better for sponge filters
- ✦During power outages (common in Cambodia), sponge filters restart within minutes of power return — canister filters may need priming
Hang-On-Back (HOB) Filters: Best Mid-Range Option
Hang-on-back filters hang on the back or side of the tank, drawing water up through an intake tube and over filter media before returning it. They are easy to set up, easy to maintain, and provide good flow rates for medium-sized tanks (40-150 liters).
HOB filters from brands like AquaClear (Fluval), Seachem Tidal, and local brands available in Phnom Penh provide excellent value. Look for models with adjustable flow rates, replaceable media compartments, and quiet operation — some cheaper models vibrate loudly on glass tanks.
The main maintenance advantage of HOB filters is ease of access — media is visible and easy to reach. The main disadvantage is that the intake pipe is a drowning hazard for small fish and bettas with long fins. Cover the intake with a fine mesh prefilter sponge.
Canister Filters: Best for Medium to Large Tanks
Canister filters are the gold standard for tanks over 100 liters. They hold far more biological media than HOB or sponge filters, run very quietly (the motor is sealed underwater or in the canister), and can be plumbed with various inlet and outlet options including spray bars and lily pipes.
Top canister brands available in Cambodia: Eheim (German, extremely reliable, 10+ year lifespan), Fluval (Canadian, good value), SunSun (Chinese, budget option that performs well if maintained). A quality canister filter for a 200-liter tank costs $60-150 USD.
Canister filters require maintenance every 4-6 weeks — less often than sponge or HOB filters because they hold more media. During maintenance, never wash all media at once. Rotate: clean the mechanical prefilter one month, leave biological media untouched; clean biological media the next month only if flow drops significantly.
- ✦Always add a coarse prefilter sponge to the canister intake — it catches debris before the canister and extends cleaning intervals
- ✦Prime canister filters by filling with water before starting — running dry damages the impeller
- ✦In Cambodia, power surges can damage electronic components — use a surge protector for canister filters
- ✦Canister filter stopped working? Check: intake clogged, air locked (fill with water then start), or impeller jammed by debris
Internal Submersible Filters: Budget Option for Small Tanks
Internal submersible filters (also called internal power filters) sit inside the tank, completely submerged. They are widely available in Cambodia at very low prices and are a good starting filter for beginners with tanks under 60 liters.
The main disadvantage of internal filters is that they take up space inside the tank and are visible. They also heat the water slightly from motor heat — a consideration in Cambodia's already-warm climate. Their mechanical filtration is often the weakest of all filter types, relying on a small foam pad that needs rinsing weekly.
For a beginner setting up their first 30-40 liter betta or guppy tank in Cambodia, a combination of one small internal filter plus one sponge filter gives excellent value and redundancy for around $10-15 USD total.
Flow Rate: How Much Is Enough?
The standard recommendation is to filter your tank volume 4-6 times per hour for tropical fish, and 8-10 times per hour for goldfish. A 100-liter betta community tank needs a filter moving at least 400-600 liters per hour.
In Cambodia, aim for the higher end of these ranges because warmer water carries less dissolved oxygen and bacteria metabolize waste faster in heat. What is adequate filtration in a 22°C German aquarium may be insufficient for your 30°C Phnom Penh tank.
More filtration is almost never harmful if designed correctly. The exception is bettas and other slow-swimming fish, which are stressed by strong surface current. In these tanks, aim for 4-5 times per hour and direct the outlet along the glass to break the current rather than across the tank.
Choosing the Right Filter for Your Situation
For a 20-40L betta or shrimp tank: one or two sponge filters. Total cost: $5-10. For a 40-100L community tank: a hang-on-back filter, 300-600 LPH. Budget: $15-30. For a 100-200L planted or cichlid tank: canister filter. Budget: $40-100. For a 200L+ goldfish tank: oversized canister plus supplemental sponge filter for extra bio-capacity.
At 4848 One Shop, we sell aquarium starter kits that include the right filter for your tank size, along with the fish that suit your setup. Browse our fish catalog or contact us on Telegram — we help you choose the right equipment before you buy.