Aquarium Filters Compared: Which Type Actually Works for Planted Tanks

Filtration is one of those topics where every aquarist has strong opinions and at least three of them contradict each other. Canister filter loyalists look down on HOB users. Sponge filter purists think everyone else is overthinking it. And somewhere in the corner, someone is running a planted tank with no filter at all and claiming the plants handle everything. The truth, as usual, lives in the middle, and depends heavily on what you are trying to achieve.

Understanding Filtration in Planted Tanks

Before comparing filter types, understand what filtration actually does in an aquascape. There are three types of filtration happening simultaneously:

• Mechanical: Physically trapping debris, detritus, and floating particles. Makes water clear.
• Biological: Beneficial bacteria converting ammonia to nitrite to nitrate. Keeps fish alive.
• Chemical: Activated carbon or specialty media removing dissolved organic compounds, tannins, medications. Optional in most planted setups.

In a planted tank, biological filtration is partially handled by the plants themselves, they absorb ammonia and nitrate directly. This means planted tanks have lower filtration demands than fish-only setups, but you still need water movement and mechanical filtration for clarity.

Canister Filters

How They Work

An external box that sits below the tank, connected by inlet and outlet hoses. Water is pulled from the tank, pushed through stacked trays of filter media, and returned via a spray bar or lily pipe. The gold standard for serious planted tanks.

Pros

• Highest media capacity of any filter type, more biological filtration
• Completely hidden from view, preserving your aquascape aesthetic
• Customizable media configuration for your specific needs
• Strong, consistent flow rate with adjustable output
• Lily pipe outlets create elegant flow patterns for CO2 distribution

Cons

• Most expensive filter type ($60 to $300+)
• Maintenance requires disconnecting hoses and opening the canister, a wet project
• Potential for leaks at hose connections if not properly maintained
• Bulky, needs space in the stand or cabinet below the tank

Hang-On-Back (HOB) Filters

How They Work

Clips onto the tank rim, draws water up through an intake tube, passes it through a media chamber, and waterfalls it back into the tank. The most common filter type in the hobby.

Pros

• Easy to install and maintain, lift the lid, swap the media
• Affordable ($15 to $60 for most sizes)
• Good mechanical and biological filtration for the price
• No risk of external leaks like canister filters

Cons

• Visible on the back of the tank, breaks the clean look of rimless setups
• Surface agitation from the waterfall return degasses CO2 from the water
• Limited media capacity compared to canisters
• Can be noisy, especially as water level drops between top-offs

Sponge Filters

How They Work

An air pump drives air through a tube inside a sponge, creating a rising column of bubbles that draws water through the sponge. Simple, effective, nearly impossible to break.

Pros

• Cheapest filter option ($5 to $15 plus an air pump)
• Excellent biological filtration, the sponge surface area houses massive bacteria colonies
• Safe for shrimp and fry, no intake to trap small creatures
• Practically no maintenance beyond occasional squeezing in old tank water
• No moving parts to fail, the air pump is the only mechanical component

Cons

• Visible in the tank and aesthetically challenging in aquascapes
• Surface agitation from bubbles drives off CO2 even more than HOB filters
• Weak flow, poor at distributing CO2 and nutrients across the tank
• Minimal mechanical filtration, water clarity suffers compared to other types

Internal Filters

How They Work

A submersible pump with attached media chamber that sits inside the tank. Some double as powerheads with filtration capabilities.

Pros

• Compact and self-contained, no external equipment
• Good flow for CO2 and nutrient distribution
• Moderate price ($15 to $40)
• Easy to hide behind hardscape in larger tanks

Cons

• Takes up space inside the tank
• Limited media capacity
• Can be difficult to hide in nano tanks
• Some models are noisy

Filter Media for Planted Tanks

Regardless of filter type, your media setup for a planted tank should be:

1. Coarse sponge: First stage, catches large debris
2. Fine filter floss: Polishes water to crystal clarity
3. Biological media: Ceramic rings, bio-balls, or Seachem Matrix for bacteria colonization
4. Skip activated carbon: Unless removing tannins or medication, carbon is unnecessary in planted tanks and may remove beneficial trace nutrients

Need to know what size filter your tank requires? Our tank size calculator gives you the exact water volume so you can match the right filter flow rate to your setup.