Last Updated: May 21, 2026
Aquarium liquid CO2 carbon supplements are the most accessible way to provide extra carbon for planted tank growth without the cost and complexity of a pressurized CO2 system. Products like Seachem Flourish Excel, Easy Carbon, and NilocG AquaticS offer a simple dose-per-gallon routine that can meaningfully accelerate plant growth and even suppress certain algae types when used consistently. Whether you’re running a low-tech planted tank or looking for a backup to your pressurized system, choosing the right aquarium liquid CO2 supplement comes down to bioavailability, dose efficiency, compatibility with your fish and invertebrates, and overall cost per treated gallon.
Quick Picks
Seachem Flourish Excel
Seachem Flourish Excel is the industry benchmark for liquid carbon supplementation in planted aquariums, using a proprietary carbon compound that plants absorb directly. Its dual role as both a carbon source and a mild algaecide — particularly against brush algae and hair algae — makes it one of the most versatile products in the planted tank hobby.
- Bioavailable carbon compound absorbed directly by plants
- Dual action as mild algaecide against brush and hair algae
- Well-documented dosing protocol with large community knowledge base
Prime API Co2 Booster Freshwater Aquarium Plant Treatment 8 Fl oz Bottle
As an Amazon Associate we earn from qualifying purchases. Product prices and availability are accurate as of the date/time indicated.
Easy Carbon by Easy Aqua Plants
Easy Carbon is a newer liquid carbon supplement from the Easy Aqua Plants brand, formulated to match Flourish Excel’s carbon availability at a noticeably lower per-dose cost. It’s gained significant traction in planted tank communities for delivering comparable plant response with fewer reported invertebrate sensitivity incidents.
- Comparable carbon bioavailability to Flourish Excel
- Lower cost per dose than most established competitors
- Reported fewer invertebrate sensitivity issues
Prime API Co2 Booster Freshwater Aquarium Plant Treatment 16 oz Bottle, Brown
As an Amazon Associate we earn from qualifying purchases. Product prices and availability are accurate as of the date/time indicated.
NilocG AquaticS Enhance Liquid Carbon
NilocG’s Enhance is a concentrated liquid carbon formula that offers an exceptional cost-per-gallon ratio, especially when purchased in larger bottle sizes. It’s a favorite among hobbyists running multiple planted tanks who need to dose carbon daily without significant ongoing expense.
- Highly concentrated formula for low cost per gallon treated
- Large bottle sizes available for multi-tank households
- Straightforward dosing without complex mixing
Prime Carbon Boost - Liquid Carbon Source for Aquarium Plants - CO2 Alternative for Faster Growth in Freshwater Tanks - Part of the Flora Nutrition Series - 4.2 fl oz
As an Amazon Associate we earn from qualifying purchases. Product prices and availability are accurate as of the date/time indicated.
Why Trust Our Recommendations
Our liquid CO2 supplement reviews are grounded in planted aquarium chemistry, practical dosing experience across low-tech and medium-tech setups, and an honest assessment of the significant hobbyist community data on plant response, algae suppression efficacy, and invertebrate compatibility. We don’t treat manufacturer dosing claims at face value — we cross-reference community testing, consider concentration differences between products, and factor in cost over time because liquid carbon supplementation is a daily or near-daily expense that compounds quickly across multiple tanks.
Detailed Reviews
1. Seachem Flourish Excel
Seachem Flourish Excel uses a molecule called polycycloglutaracetal (and related compounds) as a bioavailable carbon source. Unlike dissolved CO2 gas, which plants absorb through their leaves, Excel’s carbon compound is absorbed both through leaves and roots and processed through a different enzymatic pathway. This isn’t a direct CO2 substitute — plants still benefit more from proper CO2 injection — but for low-tech setups or tanks where pressurized CO2 isn’t practical, it provides meaningful carbon supplementation that results in noticeably improved plant growth compared to no supplementation at all. The algaecide effect is real and well-documented: spot-treating black beard algae (BBA) by directly applying Excel to affected areas with a syringe during a water change kills the algae within 24–48 hours for most hobbyists. Standard dosing is 5 mL per 50 gallons daily or at every water change. The main limitation is cost — at standard concentrations, Excel is expensive to dose daily in larger tanks. Pros: industry-proven formula, dual carbon and algae-control benefits, massive community knowledge base. Cons: expensive for large tanks, can harm some mosses (especially Riccia) and sensitive plants at overdose levels, some invertebrate sensitivity reported.
2. Easy Carbon by Easy Aqua Plants
Easy Aqua Plants has built a strong reputation for well-formulated, hobbyist-priced fertilizer and supplement products, and Easy Carbon is their answer to the expensive daily dosing cost of Flourish Excel. The active carbon compound appears to be the same class of molecules, and in side-by-side plant growth comparisons reported in planted aquarium forums, most hobbyists observe similar growth response between Easy Carbon and Excel at their respective recommended doses. The frequently reported advantage is lower invertebrate sensitivity — Excel is known to harm some shrimp species (particularly sensitive Caridina varieties) at doses above the recommended rate, and Easy Carbon users report fewer incidents. At comparable or lower cost per dose depending on bottle size, it’s become a serious challenger to Seachem’s dominance in this category. Standard dosing is approximately 1 mL per 10 gallons daily. Pros: comparable plant efficacy to Excel, lower price per dose, reportedly better invertebrate tolerance. Cons: smaller established community vs. Seachem’s decades of hobbyist data, algae-control spot-treatment less documented than Excel.
3. NilocG AquaticS Enhance Liquid Carbon
NilocG is a specialty aquatic fertilizer brand that formulates its products at higher concentrations than most retail brands, passing the cost savings to hobbyists who need to dose frequently across multiple tanks. Enhance is their liquid carbon product, and its defining advantage is the cost-per-gallon-treated calculation: in larger bottle sizes, the per-dose cost is significantly lower than Flourish Excel and competitive with Easy Carbon. The formula performs well for plant growth support in low-to-medium tech setups, and community feedback on algae suppression with direct spot application is generally positive, though the experience base is smaller than Seachem’s. For fishkeepers running 3+ planted tanks, NilocG’s economics are compelling. Pros: lowest cost per gallon treated, concentrated formula, large bottle sizes available. Cons: less name recognition means less community troubleshooting support, concentration requires careful dosing.
4. API CO2 Booster Liquid Carbon
API CO2 Booster is the most widely available liquid carbon supplement in traditional pet store chains, making it the go-to option when you need to pick up a bottle locally without waiting for an online order. The formula and mechanism are similar to Excel and Easy Carbon, and in community comparisons it performs adequately for basic planted tank support. It’s not the best value per dose compared to concentrated alternatives, and hobbyists with large or multiple tanks will find the cost adds up quickly at standard dosing rates. For single small tanks in beginner setups where convenience matters and local availability is a priority, API CO2 Booster is a practical choice. Pros: very widely available locally, trusted API brand, straightforward dosing instructions. Cons: higher cost per dose than concentrated alternatives, basic-level performance compared to premium brands.
Buyer’s Guide
Liquid CO2 vs. Pressurized CO2: Honest Comparison
Liquid carbon supplements are not a true substitute for pressurized CO2 injection. Pressurized systems deliver dissolved CO2 gas directly to the water column where plants absorb it in the same form used in photosynthesis, typically achieving 20–30 ppm dissolved CO2 in a well-tuned system. Liquid carbon works through a different biochemical pathway and the amount of carbon made available per dose is significantly lower on a molar basis. The result is that liquid carbon supports meaningful plant growth in low-demand setups and with slow-growing plants, but cannot support the high growth rates achievable with proper CO2 injection. Think of liquid carbon as a supplement that bridges the gap rather than a direct replacement — it’s what you use when pressurized CO2 isn’t practical for your setup.
Dosing Per Gallon: How to Calculate Correctly
Dose liquid carbon based on net water volume, not tank capacity. A 29-gallon tank with substrate, hardscape, and decorations holds roughly 22–25 gallons of water, not 29. Overdosing liquid carbon is a real risk: at 2–3x the recommended dose, most liquid carbon products can cause noticeable stress to shrimp, snails, and some sensitive fish. Moss species are particularly sensitive — Riccia fluitans and some Fissidens species can melt back from even moderate overdoses of glutaraldehyde-based products. If your tank contains sensitive invertebrates or rare mosses, start at half the recommended dose and observe for a week before increasing.
Algae Control: When to Spot-Treat vs. Dose Tank-Wide
Liquid carbon’s algaecide effect can be used in two ways: tank-wide dosing at the daily maintenance rate provides ongoing mild suppression that gradually weakens certain algae types, and direct spot-treatment applies a concentrated dose to a specific algae colony during a water change. Spot-treatment is most effective against black beard algae (BBA) and staghorn algae — use a 5 mL syringe to apply undiluted product directly to the algae mass while the tank water level is lowered, then refill after 2–3 minutes of contact time. Do not leave high-concentration liquid carbon in contact with sensitive plants, shrimp, or small fish — the exposure-during-water-change method limits risk while maximizing efficacy.
Frequently Asked Questions
Is liquid CO2 safe for shrimp tanks?
At the recommended daily dose, most liquid carbon products are safe for Neocaridina shrimp (red cherry shrimp, blue dream, etc.) in tanks that are otherwise well-maintained. Caridina shrimp (crystal red, crystal black, Taiwan bee variants) are significantly more sensitive and have shown more frequent reactions to glutaraldehyde-based products. If you keep Caridina shrimp, either use Easy Carbon (which has a better invertebrate tolerance reputation) at half the recommended dose, or avoid liquid carbon entirely and focus on other plant growth methods. Always dose slowly — add to high-flow areas rather than directly above shrimp colonies.
How often should I dose liquid carbon?
Most liquid carbon products are dosed daily or at every water change for continuous plant support. Daily dosing produces better results than every-other-day or weekly dosing because the carbon compound is consumed by plants and metabolized by tank bacteria within 24 hours. If daily dosing is inconvenient, dosing with every water change (typically 2–3 times per week) is a reasonable compromise that provides most of the benefit at reduced inconvenience. Dosing frequency should remain consistent — starting and stopping liquid carbon supplementation abruptly causes plant growth rate fluctuations that can create algae openings.
Can I use liquid carbon alongside pressurized CO2?
Yes, some advanced planted tank hobbyists use liquid carbon as a supplement to pressurized CO2, particularly for its algae-control properties rather than its carbon contribution. When using both, be aware that the combined carbon and bioactive components can stress invertebrates more than either product alone. In high-tech setups with pressurized CO2, the primary motivation for adding liquid carbon is usually targeted black beard algae treatment rather than plant nutrition, since the CO2 injection already provides ample dissolved carbon.
Does liquid CO2 affect pH or KH like pressurized CO2?
No — one of the key differences between liquid carbon supplements and pressurized CO2 is that liquid carbon products do not dissolve as CO2 gas and therefore do not lower pH or carbonate hardness (KH). Pressurized CO2 forms carbonic acid in water, causing pH to drop in proportion to CO2 concentration — this pH swing is both a useful growth signal and a risk if CO2 is overdosed overnight. Liquid carbon has a negligible effect on pH and KH, making it safer for tanks with pH-sensitive fish or in setups where stable water chemistry is critical.
Final Verdict
Seachem Flourish Excel remains the go-to aquarium liquid CO2 carbon supplement for most planted tank hobbyists, backed by two decades of documented efficacy and one of the most supportive hobbyist knowledge communities in the aquarium world. For shrimp-keeper plants and cost-sensitive multi-tank setups, Easy Carbon’s better invertebrate tolerance and lower price make it a compelling alternative worth trying. NilocG Enhance wins on pure economics for hobbyists dosing multiple tanks daily. Whichever product you choose, consistent daily dosing and correct net-volume calculation are what separate successful liquid carbon use from frustrating, inconsistent results.
