The best liquid carbon supplements for planted tanks in 2026
Liquid carbon is the no-equipment way to give a low-tech planted tank a carbon boost — a daily cap in the water, no cylinder, no risk of gassing fish. Be honest about the limit, though: it helps easy and mid-demand plants but will not carry a demanding carpet or a high-light aquascape. For that you need pressurised gas.
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Frequently asked questions
Is liquid carbon a real substitute for pressurised CO2?
Not fully. Liquid carbon provides a bioavailable carbon source that helps many plants, but it cannot match the dissolved CO2 a pressurised system delivers and will not support demanding carpets or high-light tanks. Think of it as a helpful boost for low-tech setups, not a true replacement — if you want a lush, pearling high-tech scape, you need real gas.
Does it need dosing every day, and can I overdose it?
Yes, and yes. Liquid carbon breaks down within about 24 hours, so it only works if you dose daily. At the recommended dose it's fine for most tanks, but higher doses can melt sensitive plants like Vallisneria and mosses and stress shrimp and delicate fish. Start at half the label dose, watch your plants and livestock for a week, then increase slowly.
Can liquid carbon help with algae?
Seachem Flourish Excel in particular doubles as an algae spot-treatment: dosed directly onto affected leaves or hardscape with the filter briefly off, it damages many soft algae like BBA. It's a useful side benefit, not a whole-tank cure — the real fix for algae is balancing light, nutrients and a sensible 6–8 hour photoperiod.
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