Seachem Flourish Excel Review
A bioavailable liquid carbon source dosed daily — a genuine help for low-tech planted tanks and a useful spot-treatment for algae, but an honest step below true pressurised CO2.
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👍 Pros
- No cylinder, regulator or gas — just a daily cap dosed into the tank
- Noticeably improves growth on easy and mid-demand plants in low-tech setups
- Doubles as an algae spot-treatment when dosed directly onto problem spots
- Cheap to start and completely avoids any risk of gassing your fish
👎 Cons
- Not true CO2 — it will not support demanding carpets or high-light aquascapes
- Must be dosed every day and breaks down within about 24 hours
- Overdosing can harm sensitive plants (Vallisneria, mosses) and stress livestock
What liquid carbon actually does
Seachem Flourish Excel supplies carbon in a bioavailable liquid form that plants can use, dosed once a day straight into the tank. On a low-tech setup — modest light, easy-to-mid plants — it delivers a real, visible improvement in growth and health without any cylinder, regulator or risk of over-gassing your fish. It is the lowest-effort way to give plants a carbon boost, and many keepers run it for years on tanks that would never justify a full CO2 rig.
Where it falls short
Be honest with yourself about its limits. Liquid carbon is not true CO2: it will not support a demanding carpet, a high-light aquascape or the fastest-growing stem plants, and it breaks down within about a day so it must be dosed daily to do anything. It can also be overdone — higher-than-label doses melt sensitive species like Vallisneria and mosses and can stress shrimp, so start low. Used as directed it doubles neatly as an algae spot-treatment, dosed directly onto affected leaves or hardscape with the pump briefly off.
How it fits with our other CO2 picks
If your ambitions grow past what liquid carbon can do, the reliable next step is a pressurised system — start with the all-in-one FZONE compact CO2 kit or the dual-stage CO2Art Pro-SE regulator, and add a NilocG glass drop checker to keep it safe. Compare every option on our CO2 systems hub, and pair it with the right lighting and plant fertilizers for your tank.
The easiest way to help a low-tech planted tank and a handy algae spot-treatment — as long as you go in knowing it is a supplement, not a stand-in for real pressurised CO2.
Seachem Flourish Excel — 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 it does not support demanding carpeting plants 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 tank, you need pressurised gas.
How does it compare to DIY CO2 and a pressurised kit?
Liquid carbon is the simplest option: no equipment, no gassing risk, just a daily dose. DIY yeast CO2 adds real gas but is inconsistent and stops overnight. A pressurised kit with a solenoid on a timer and a drop checker is the reliable, controllable route and the only one that fully unlocks demanding plants. Choose by how far you want to push the tank.
Can I overdose it, and is it safe for fish and shrimp?
Yes, you can overdose it. At the recommended dose it is fine for most tanks, but higher doses can melt sensitive plants like Vallisneria and mosses and stress shrimp and sensitive fish. Start at half the label dose, watch your plants and livestock, and increase slowly.
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