Seachem Flourish Excel Liquid Carbon Review: Glut Alternative
Few aquarium products divide hobbyists like this blue-capped bottle. A proper Seachem Flourish Excel liquid carbon review has to address both the loyal following that credits it with carpet-plant miracles, and the sceptics who see it as dilute glutaraldehyde sold at a premium. This guide from Gensou Aquascaping at 5 Everton Park draws on years of dosing Excel across Singapore HDB low-tech tanks and CO2-injected competition scapes, and gives a practical take on where it earns its place.
What Excel Actually Contains
The active ingredient is polycycloglutaracetal, a polymerised form of glutaraldehyde, present at roughly 1.5 percent. Seachem have never confirmed this on the label, but the identification is well established through independent analysis. Plants take up the compound and process it through an enzymatic pathway that ultimately liberates carbon useful for photosynthesis, which is why it is marketed as bioavailable carbon rather than as a biocide.
The Glutaraldehyde Alternative Question
DIY glutaraldehyde at industrial strength is sold online and in reef shops for a fraction of the Excel cost. You can dilute it to match Excel strength if you know what you are doing, but the margin for error is uncomfortable, especially when dosing in a tank with shrimp. Excel gives you a premixed, stabilised product with a known concentration and a cap that dispenses in measured pumps. Our glutaraldehyde dosing guide covers the raw-chemical route for keepers who accept the risk.
Does It Really Work as Carbon
For low-tech tanks without CO2 injection, yes, modestly. Excel closes some of the gap between atmospheric CO2 and what plants actually need for reasonable growth. You will see faster Anubias leaf turnover, healthier Java fern fronds and more colour in stem plants. It is not a substitute for pressurised CO2 in a high-light tank, and anyone who tells you they grew Monte Carlo to carpet using Excel alone likely had exceptional light, nutrient and flow conditions in parallel.
Algae Control Side Effect
The use most keepers actually care about is spot-dosing on black beard algae, staghorn and some filamentous species. Turn the filter off, draw Excel into a syringe, and squirt directly onto the affected area. Within 24 to 48 hours the algae will flush pink then white. Our black beard algae removal guide and the complete BBA protocol walk through the technique. This algaecide behaviour is not officially marketed, but it is the reason many Singapore keepers keep a bottle on the shelf.
Sensitive Plants and Shrimp
Excel is not universally safe. Vallisneria, Egeria, some mosses and Riccia can melt at full label dose, and should be introduced gradually at half rate. Shrimp are generally fine at label dose if you ramp slowly, but overdosing will wipe out a neocaridina colony overnight. Never double-dose to catch up after a missed day. Singapore hobbyists running cherry shrimp alongside BBA problems should spot-dose only, with filter off and a small water change after.
Dosing Schedule in Practice
Label dose is 5 ml per 200 litres daily, with an initial or post-water-change dose of 5 ml per 40 litres. In practice, most balanced tanks run better at label rate daily rather than the heavier initial dose. For a 60 litre HDB nano that works out to about 1.5 ml a day, easily tracked with the graduated cap. Combine with a consistent dosing schedule alongside your macros and traces, following the framework in our EI dosing guide.
Compatibility With Other Seachem Products
Excel is stable with Flourish Comprehensive, Potassium, Nitrogen and Phosphorus, but best dosed at least six hours apart from Flourish Iron to avoid oxidation interactions. Never mix Excel directly with hydrogen peroxide, potassium permanganate or any medication containing formaldehyde, which it can cross-react with. If you run a parallel Flourish Comprehensive dosing routine, time Excel in the morning and traces in the afternoon.
Price Per Dose in Singapore
A 500 ml bottle retails for around $22 to $28, which dosed at 1.5 ml daily on a nano lasts almost a year. A 2 litre bottle at $60 to $75 is better value for anyone running a 200 litre display or multiple tanks. Shopee and Lazada sellers occasionally discount to around $18 for a 500 ml during sale events; just check expiry dates because Excel loses potency after roughly 18 to 24 months from manufacture.
When Excel Is the Wrong Product
If your tank has injected CO2 running at a proper drop checker green, Excel adds very little. If your algae problem is green dust or green spot, Excel will not touch it and you should address light intensity, nutrients or the green spot algae fix instead. If you keep a heavy Vallisneria jungle, Excel will melt it no matter how slowly you ramp.
Verdict
Excel is a genuinely useful product for low-tech Singapore tanks and for BBA spot-dosing, and it remains one of the more reliable ways to get moderate growth without the commitment of pressurised CO2. Buy the large bottle if you run more than 100 litres, keep it out of Vallisneria tanks, and treat the algaecide effect as a bonus rather than a primary reason to dose. Plants that want CO2 eventually need CO2.
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