How to Use Purigen in a Planted Aquarium: Dosing and Recharging
Crystal-clear water that lets light penetrate to carpet plants is every aquascaper’s goal, and Seachem Purigen is one of the most effective tools for achieving it. Understanding how to use Purigen in a planted aquarium correctly, including dosing volume, placement and the all-important recharging cycle, will save you money and keep your water polished for months. This is a product we rely on daily at Gensou Aquascaping, 5 Everton Park, Singapore, across tanks ranging from 20-litre nanos to 400-litre display scapes.
What Purigen Actually Does
Purigen is a synthetic adsorbent, not a resin or carbon. It removes dissolved organics, tannins and nitrogenous waste from the water column at a molecular level. Unlike activated carbon, it does not strip trace elements or fertiliser micro-nutrients that your plants need. The result is water clarity that rivals a sterile display without the nutrient penalty. Fresh Purigen beads are white; as they exhaust, they darken through amber to dark brown, giving you a visible indicator of when to recharge.
Correct Dosing for Planted Tanks
Seachem’s recommendation is 100 ml of Purigen per 400 litres. For a typical 60 cm planted tank holding around 50-60 litres, a single 100 ml bag is more than enough. Over-dosing is not harmful, but it offers diminishing returns and means more frequent recharging. In heavily stocked or tannin-rich blackwater-style setups, you may exhaust a bag in three to four weeks. A lightly stocked aquascape with minimal driftwood can go eight weeks or more before the beads turn dark.
Where to Place It in Your Filter
Purigen should sit after your mechanical filtration media so that debris does not clog the bag prematurely. In a canister filter, place the bag in the final media tray before the outlet. For hang-on-back filters, wedge the bag between the sponge and the outflow. Avoid putting Purigen directly in the tank as a reactor bag, since inconsistent flow through the beads reduces efficiency. Good contact time with moving water is key.
Recharging With Bleach
Soak the exhausted bag in a solution of one part plain, unscented household bleach (sodium hypochlorite, no surfactants) to one part water for 24 hours. The beads will return to bright white. Rinse the bag thoroughly under tap water, then soak it in a solution of dechlorinator, roughly five times the normal dose, for at least eight hours. Rinse once more and sniff the bag: if any chlorine odour remains, repeat the dechlorinator soak. In Singapore, where PUB water is treated with chloramine, an extra rinse cycle is a wise precaution.
How Many Times Can You Recharge
Seachem states Purigen can be recharged indefinitely, and in our experience at Gensou Aquascaping it remains effective for well over a dozen cycles. Eventually the beads may not return to pure white and adsorption slows. At that point, a fresh 100 ml bag costs around $12-15 on Shopee or Lazada, making it one of the most cost-effective filtration products available.
Impact on Fertilisation
A common concern is whether Purigen strips liquid fertilisers. The short answer is no, at least not meaningfully. Potassium, iron chelates and other plant micro-nutrients pass through largely unaffected. What Purigen does remove are dissolved organic compounds that, if left unchecked, feed algae and create a yellowish tint. Your plants continue to receive their nutrients while algae loses a food source. If you dose Excel or liquid carbon, add it at least 30 minutes before lights-on so it can act on algae before Purigen has a chance to adsorb any residual.
When Not to Use Purigen
If you are intentionally running a blackwater aquarium with catappa leaves and peat, Purigen will strip the very tannins you want. Similarly, if you are using medication that relies on staying dissolved in the water column, remove Purigen for the duration of treatment. Outside those specific scenarios, Purigen is a reliable addition to any planted aquarium filtration system and one of the simplest upgrades for water clarity you can make.
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emilynakatani
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