Best Reactors for Aquariums: CO2 and Phosphate Media Reactors
Choosing the best reactor aquarium CO2 phosphate media setup is critical for planted tank success. Reactors dissolve CO2 completely or tumble chemical media to remove excess phosphate, giving you precise control over water chemistry. At Gensou Aquascaping Singapore, based at 5 Everton Park with over 20 years of hands-on experience, we rely on reactors across our client installations and our own display tanks. Here is what we recommend.
What Aquarium Reactors Actually Do
A reactor is a sealed chamber connected inline with your canister filter or a dedicated pump. Water flows in, contacts gas or media inside, and exits with the dissolved product or minus the unwanted compound. Unlike passive diffusers or bags of media dropped into a filter, reactors maximise contact time and efficiency.
Two types dominate the planted aquarium hobby: CO2 reactors and phosphate media reactors. Some hobbyists run both on the same system.
CO2 Reactors Versus Ceramic Diffusers
Ceramic diffusers are popular, but they waste CO2. Tiny bubbles that reach the surface escape into the atmosphere. A well-designed CO2 reactor achieves near 100% dissolution because gas is trapped inside the chamber and forced into contact with turbulent water. For tanks above 150 litres, the efficiency gains alone justify the higher upfront cost.
Reactors also eliminate the unsightly mist of micro-bubbles that some aquascapers dislike. Water exits the reactor crystal clear and fully saturated with CO2.
Top CO2 Reactor Picks
The GLA Atomic Inline CO2 Diffuser-Reactor hybrid remains a strong choice. Priced around $45-$65, it fits 12/16 mm or 16/22 mm hosing and uses an internal ceramic disc combined with a vortex chamber. Dissolution rates exceed 95% at moderate flow.
For larger systems, the Sera Flore CO2 Reactor 500 handles tanks up to 600 litres. Its counter-current design forces CO2 upward against downward-flowing water, ensuring complete absorption. Expect to pay $70-$100. Availability in Singapore varies, but Carousell sellers and specialty shops at Seaview Aquarium often stock them.
Budget-conscious hobbyists can build an effective DIY reactor from a clear acrylic tube, two barb fittings, and bio-balls inside. Total cost: under $15. Performance rivals commercial units when sized correctly.
Phosphate Media Reactors Explained
Excess phosphate fuels algae growth. Singapore’s PUB tap water, while soft and slightly acidic, occasionally carries measurable phosphate levels depending on reservoir source and season. A phosphate reactor tumbles granular ferric oxide (GFO) media in a controlled flow, binding PO4 efficiently.
Unlike placing GFO in a mesh bag inside your filter, a reactor prevents channelling — water cannot bypass the media by flowing around it. Every drop contacts the granules.
Top Phosphate Reactor Picks
The Two Little Fishies Phosban Reactor 150 is an industry standard. At around $50-$70, it holds up to 200 g of GFO media and suits tanks from 100 to 400 litres. A small powerhead drives water through the chamber at adjustable flow rates.
For nano setups under 80 litres, the Aqua Design Amano NA Reactor or similar compact inline units work well. They attach directly to canister filter tubing without needing a separate pump, saving space — important for HDB setups where cabinet room is limited.
Refill GFO media every 4-8 weeks depending on your phosphate load. A TDS or phosphate test kit helps you determine the ideal replacement schedule. Budget roughly $20-$30 per refill batch.
Installation and Flow Rate Guidelines
CO2 reactors perform best at moderate flow — around 200-500 litres per hour for tanks up to 300 litres. Too much flow pushes undissolved gas out the exit. Too little allows CO2 to accumulate and form a large pocket inside, reducing efficiency.
Phosphate reactors need gentle flow to tumble GFO without pulverising it into dust. Aim for a slow, visible tumble — the granules should gently roll, not violently churn. Crushed GFO releases iron particles that cloud your water and can harm sensitive shrimp.
Running Both Reactors on One System
If your canister filter provides at least 800 litres per hour of output, you can split the outflow using a Y-connector with individual tap valves. One line feeds the CO2 reactor, the other feeds the phosphate reactor. Both return lines merge before entering the tank. This keeps each reactor at its optimal flow rate independently.
Alternatively, run the CO2 reactor inline on the main return and use a small dedicated powerhead for the phosphate reactor. This approach gives you more precise control and avoids reducing your main filter flow.
Maintenance and Troubleshooting
CO2 reactors need occasional cleaning. Bio-film builds up inside, reducing turbulence and dissolution. Disassemble and scrub with a bottle brush every 2-3 months. Check O-rings for cracks — a leaking reactor can dump CO2 directly into air instead of water, wasting gas and dropping your pH inconsistently.
Phosphate reactor media must never run dry. If you switch off the pump for maintenance, close the valves to keep water inside. Dried GFO crumbles and becomes useless. Mark your calendar for media replacement — consistency keeps algae at bay and your aquascape thriving.
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