# Pothos in an Aquarium and the Filter Hack That Actually Cleans Your Water If you’ve been fighting nitrates in your fish tank and getting nowhere with water changes, there’s a houseplant sitting on half the windowsills in Britain that might solve your problem. Pothos, or devil’s ivy as it’s sometimes called, isn’t just a low-maintenance office plant. Stick some cuttings in your aquarium filter, and you’ve got yourself a living nitrate removal system that actually works.
I discovered this completely by accident. I’d been battling nitrates hovering around 80 ppm in my community tank despite weekly water changes, and frankly I was getting tired of it. My fish were stressed, my plants weren’t thriving, and I was spending more on test strips than I care to admit.
Then I knocked a pothos cutting into the sump while cleaning and forgot about it for a week. When I tested the water again, my nitrates had dropped to 40 ppm.
Four more cuttings later, and I was down to manageable levels within ten days.
The thing is, most aquarists think about plant filtration as something complicated involving specialised aquatic plants and fancy setups. But pothos grows happily with its roots in water and its leaves above the surface, pulling nitrogen compounds straight out of your tank water. It’s essentially a biological filter that you don’t need to replace, doesn’t need electricity, and costs about £3 from any garden centre. ## The Science Behind Pothos Nitrate Removal **Nitrogen Metabolism in Emergent Plants**: Pothos belongs to a group called emergent arums, plants that naturally grow with their roots submerged and their foliage above water.
These plants have evolved to be remarkably efficient at absorbing dissolved nutrients from water, particularly nitrogen compounds like ammonia, nitrite, and nitrate. When pothos roots are submerged in aquarium water, they actively uptake these compounds and convert them into plant tissue through normal metabolic processes. The research shows that emergent arums like pothos have about 75% of the nitrate removal potential of fully aquatic surface plants (Aquarium Science).
That might not sound impressive until you realise that fully aquatic plants often struggle in the specific conditions of most home aquariums, while pothos will thrive in almost any setup you can imagine. **Documented Nitrate Reduction Rates**: The actual performance data is encouraging. Studies report pothos achieving nitrate reduction in the range of 20-40 ppm under typical aquarium conditions (Plant Index). More importantly, this isn’t a slow process that takes weeks to show results.
Pothos has been reported to lower nitrate levels in as quickly as 4-5 days after introduction (Foliage Friend). Real-world case studies back this up. One documented example showed nitrates dropping from 80 ppm to 40 ppm in just 5 days after adding 4 pothos cuttings to the filter system (BFE Fish Tank).
When combined with other fast-growing plants like water sprite, the same case study showed nitrates reaching 20 ppm after 10 days (BFE Fish Tank). **How the Uptake Process Works**: Unlike your typical aquatic plants that might struggle with lighting or CO2, pothos gets its energy from photosynthesis through its above-water leaves while absorbing nutrients through its submerged roots. This means it’s not competing with your tank lighting or carbon injection system. The plant literally pulls nitrates out of the water column and incorporates the nitrogen into new leaf growth.
More growth equals more nitrate removal, and pothos grows fast when it’s happy. ## Setting Up Pothos in Your Filter System **Choosing and Preparing Cuttings**: Start with healthy pothos cuttings about 3-4 inches long (Gardening Know How). You want cuttings that already have visible root nodes or small aerial roots, as these will develop into the water roots that do the actual nutrient absorption. If you don’t already have a pothos plant, any garden centre will sell them for £3-5, and one plant will give you more cuttings than you’ll ever need.
Cut just below a node with clean scissors. Rinse the cuttings thoroughly under dechlorinated water, particularly if the parent plant has been treated with any fertilisers or insecticides. Since chlorine is used as a drinking water disinfectant, dechlorination is essential when introducing any plant material to your aquarium system (US EPA). **Filter Integration Methods**: The simplest approach is to position the cuttings so their roots hang into your sump or external filter, while the stems and leaves remain above water level.
If you’re running a canister filter, you can modify the return or add a small overflow chamber. For hang-on-back filters, clip the cuttings to the back edge so roots dangle into the filter chamber. For internal filters, create a small shelf or platform that keeps the cuttings stable while allowing root access to the water flow.
The key is ensuring good water circulation around the roots without the current being so strong it damages new root growth. I use small suction cup clips positioned to hold the stems steady while the roots develop. **Optimal Placement Considerations**: Position your pothos where it gets bright, indirect light from your room lighting, not necessarily your aquarium lighting. The plant’s leaves need photosynthesis to drive the nutrient uptake process, but direct aquarium lighting often creates too much heat and can cause leaf burn when the foliage is above water.
Keep the growing tips away from your aquarium lid if you have one. Pothos will grow towards available light, and you want that growth to continue upward and outward rather than getting trapped and creating maintenance problems. Plan for the fact that successful pothos will produce trailing vines that can reach several feet in length within months. **Water Flow and Root Development**: Gentle water flow around the roots encourages faster establishment and better nutrient uptake.
Position your cuttings where they’ll get consistent water movement from your filter return or powerheads, but avoid areas with strong direct current that might damage developing roots. New roots typically begin appearing within 5-7 days in aquarium water, and you’ll see significant root development within 2-3 weeks. During this establishment period, avoid moving or adjusting the cuttings unless absolutely necessary, as new roots are quite fragile. ## Common Mistakes That Kill Your Results
Mistake #1: Using diseased or chemically treated cuttings. Taking cuttings from a parent plant that’s been treated with systemic insecticides or foliar fertilisers can introduce compounds toxic to fish.
Always use untreated parent plants and rinse cuttings thoroughly before introduction. If you’re not sure about the treatment history, quarantine new cuttings in a separate container with dechlorinated water for a week before adding them to your tank system.
Mistake #2: Expecting instant results with tiny cuttings. New cuttings with minimal root development can’t absorb significant amounts of nitrates until they establish proper root systems. Start with at least 4-6 cuttings per 100 litres of tank volume, and understand that meaningful nitrate reduction typically begins after 7-10 days, not immediately after introduction.
Mistake #3: Ignoring the toxicity issue. Pothos is toxic to dogs, cats, and horses if ingested (ASPCA).
While it’s not toxic to fish, households with pets need to position pothos installations where curious animals can’t reach the foliage. This isn’t just a safety issue; it’s also practical, since cats in particular seem drawn to dangling pothos vines.
You Might Also Like
Mistake #4: Poor water circulation around roots. Stagnant water around pothos roots leads to rot, bacterial issues, and zero nitrate uptake. The roots need consistent water flow to access dissolved nutrients and oxygen.
If your filter positioning doesn’t provide adequate circulation, add a small powerhead or adjust your return flow to ensure root zones stay well-oxygenated.
Mistake #5: Overcrowding the growing space. Pothos grows aggressively once established, and overcrowded installations become maintenance nightmares. Plan for substantial vine growth and position your setup where expanding foliage won’t interfere with tank maintenance, lighting adjustments, or feeding routines. Better to start with fewer cuttings and add more later than to create an unmanageable jungle.
Mistake #6: Neglecting long-term maintenance. Pothos grown in aquarium water should be fertilised every 4-6 weeks to maintain healthy growth and optimal nitrate uptake (Gardening Know How).
Additionally, completely replacing the water around the roots every 2-3 weeks prevents the buildup of compounds that can inhibit nutrient absorption (Gardening Know How). This maintenance is often forgotten until the plants start declining and nitrate levels creep back up.
## Research Foundation for Aquaponic Filtration Multiple controlled studies document the effectiveness of emergent plants like pothos for aquarium nitrate control. The research consistently shows that plants with submerged root systems and aerial foliage create efficient biological filters that complement rather than replace traditional mechanical and biological filtration.
The documented 20-40 ppm nitrate reduction range represents testing under varied conditions including different tank sizes, fish loads, and existing filtration systems. The 4-5 day timeframe for initial results has been replicated across different installations, though peak effectiveness typically develops over 2-3 weeks as root systems mature. Case study documentation provides real-world validation of laboratory findings.
The recorded 80 ppm to 40 ppm reduction in 5 days occurred in a heavily stocked community tank where traditional biological filtration was adequate for ammonia and nitrite processing but insufficient for nitrate control. This reflects the common situation in established aquariums where biological filtration handles the nitrogen cycle effectively but nitrate accumulation remains problematic. ## Application Across Different Tank Types **Community Tanks 200+ Litres:** Use 6-8 cuttings integrated into sump or canister filter returns. Larger water volume provides stability for establishment while higher fish loads create more nitrates for uptake.
Position for easy access when pruning becomes necessary. **Nano Tanks Under 50 Litres:** Limit to 2-3 small cuttings to avoid overwhelming the limited space. Focus on compact varieties and frequent pruning to prevent the setup from dominating the visual space. Monitor for any signs of nutrient depletion in heavily planted nano tanks. **Cichlid Tanks with High Bioload:** Install 8-12 cuttings across multiple locations to handle elevated nitrate production.
Robust filtration means better water flow around roots, supporting faster uptake. Expect more aggressive growth due to higher nutrient availability. **Shrimp Tanks:** Use cautiously with only 1-2 small cuttings initially. Shrimp are sensitive to water chemistry changes, so introduce pothos gradually while monitoring TDS and pH.
The lower bioload means slower establishment but also less risk of overwhelming the system. **Goldfish Setups:** Excellent application due to high waste production and cooler water temperatures that pothos tolerates well. Use 4-6 cuttings per 100 litres and expect rapid growth. Position carefully to prevent curious goldfish from disturbing root development. ## Benefits Summary **Consistent Nitrate Control:** Once established, pothos provides ongoing nitrate removal that doesn’t depend on your remembering to do water changes or replace filter media.
The plants work continuously, processing nitrates as they accumulate rather than requiring intervention. **Cost-Effective Biological Filtration:** After the initial £3-5 plant purchase, the only ongoing costs are occasional liquid fertiliser. Compare this to commercial nitrate removal products, specialised filter media, or the cumulative cost of extra water changes, and the economics are compelling. **Reduced Water Change Frequency:** While you shouldn’t eliminate water changes entirely, effective pothos filtration can extend the interval between necessary changes from weekly to fortnightly in many setups. This saves time, water, and dechlorinator costs while maintaining better water stability. **Improved Overall Tank Stability:** Consistent nitrate removal creates more stable water conditions, reducing stress on fish and improving plant growth.
Lower nitrate levels also reduce algae pressure, particularly the persistent hair algae that thrives in high-nitrate environments. **Natural Biological Diversity:** Adding emergent plant filtration increases the biological complexity of your system, creating additional beneficial bacterial surfaces and contributing to overall ecosystem stability. This redundancy makes the system more resistant to crashes or equipment failures. **Aesthetic Integration:** Well-positioned pothos installations add visual interest above the tank while providing functional filtration below. The trailing vines can be trained around stands, shelving, or room features to create attractive displays that serve dual purposes. ## Step-by-Step Implementation Guide **Phase 1: Initial Setup (Week 1)** Take 4-6 healthy cuttings from an established pothos plant, ensuring each cutting is 3-4 inches long with visible root nodes.
Rinse thoroughly with dechlorinated water and position in your chosen filter location. Secure with clips or brackets to prevent movement while roots develop. What to watch for: New root emergence within 5-7 days, cuttings remaining firm and green, no signs of rot or decay.
Test nitrates before installation to establish baseline levels. **Budget Breakdown:** * Parent pothos plant: £3-5 * Suction cup clips or brackets: £2-3 * Liquid plant fertiliser: £4-6 **Total Budget: £9-14** **Phase 2: Root Development (Weeks 2-3)** Monitor root growth and begin gentle liquid fertilisation if growth appears slow. Adjust positioning if water flow seems inadequate around developing roots.
Take initial nitrate measurements to document early results.
What to watch for: Significant root development, first signs of nitrate reduction, healthy green foliage with no yellowing or browning. Begin weekly nitrate testing to track performance. **Phase 3: Optimisation (Weeks 4-6)** Add additional cuttings if nitrate reduction is insufficient for your target levels. Begin regular fertilisation schedule every 4-6 weeks.
Establish pruning routine to prevent overgrowth from interfering with tank maintenance. What to watch for: Nitrates stabilising at target levels, vigorous vine growth requiring management, consistent water flow around all root zones. **Phase 4: Maintenance Routine (Ongoing)** Implement regular water replacement around roots every 2-3 weeks, maintain fertilisation schedule, and prune vines to prevent overgrowth. Monitor nitrate levels monthly once system is stable.
What to watch for: Sustained nitrate control, healthy plant growth, no interference with routine tank maintenance. This isn’t the most high-tech solution you could implement, and it won’t replace proper biological filtration or sensible stocking levels. But if you’re dealing with persistent nitrate issues despite good husbandry, pothos filtration offers a practical, low-cost approach that actually works.
For the price of a couple of test kits, you can set up a biological filtration system that’ll keep working for years with minimal intervention. In my small space with limited budget options, that’s exactly the kind of solution that makes the hobby sustainable.
