Flourish Excel and the Liquid Carbon Debate That Divides the Entire Hobby

# Flourish Excel and the Liquid Carbon Debate That Divides the Entire Hobby I’ve been keeping planted tanks for three years now, and there’s one bottle that sits on my shelf looking more controversial than it has any right to. Half the hobby swears by it. The other half thinks it’s overpriced snake oil that kills more plants than it helps.

The bottle in question is Seachem’s Flourish Excel, and honestly, I still don’t know which camp I’m in. I bought my first bottle after watching my red plants fade to green and reading endless forum threads about liquid carbon being the answer to everything. That was eighteen months ago.

I’ve used it religiously, stopped using it completely, started again, and switched between more CO2 setups than I care to admit. What I can tell you is this: Excel is probably the most misunderstood product in planted tank keeping, and the arguments about it say more about how we approach this hobby than they do about the product itself. ## Quick Reference | **Type** | **Suitable Tank Size** | **Price Range (£)** | **Key Feature** | **Warranty** | **Our Rating** | |———-|————————|———————|—————–|————–|—————-| | Liquid Carbon Supplement | Any size | £8-25 per bottle | Daily dosing alternative to CO2 | Standard consumer | 6/10 | ## What Excel Actually Is (And What It Isn’t) Let me start with what Excel actually contains, because half the arguments about it stem from people not understanding what they’re putting in their tanks.

Excel contains 1.5% polycycloglutaracetal (Seachem), which is a complex polymer that breaks down in water to release compounds that plants can use for photosynthesis.

It’s not liquid CO2, despite what every aquatics shop worker has probably told you at some point. CO2 is a petrol. You can’t bottle it as a liquid at room temperature without serious pressure equipment.

Excel was introduced in the early 2000s (Seachem) as an alternative carbon source for planted tanks. The idea was simple enough: give plants the carbon they need without having to mess about with CO2 cylinders, bubble counters, and drop checkers. Dose it daily, watch your plants grow better, job done.

If only it were that straightforward. The dosing is specific and matters more than most people realise. You start with 5ml per 40 litres on day one (Seachem), then drop to a maintenance dose of 5ml per 200 litres daily (Seachem).

One capful equals 5ml (Seachem), which is handy because most of us can’t be bothered with syringes for daily dosing. A 500ml bottle treats approximately 20,000 litres at maintenance dosing (Charterhouse Aquatics), which sounds impressive until you work out that it’s about four months’ worth for a typical community tank. The problem is that Excel sits in this awkward middle ground between being a supplement and being a replacement for proper CO2 injection.

It’s not quite either, and that’s where the arguments start. ## Why People Love It (And Why They’re Sometimes Right) I’ll give credit where it’s due: Excel can make a real difference in the right circumstances. In my 90-litre setup with medium light and no CO2, adding Excel noticeably improved plant growth within about three weeks. The Anubias put out new leaves faster, the Java fern looked healthier, and most importantly, the few red plants I was trying to keep actually stayed red instead of fading to brown.

The convenience factor is huge. Liquid carbon products are often dosed daily in planted tanks (Aquascaping Love), and there’s something appealing about a simple daily routine instead of managing CO2 equipment. No cylinders to refill, no solenoids to worry about, no checking if your bubble counter is still bubbling at the right rate.

Just squeeze a capful into the tank each morning and get on with your day. For beginners especially, Excel removes one major barrier to keeping plants successfully. CO2 injection intimidates a lot of people, and rightly so.

Get it wrong and you can petrol your fish overnight. Excel might not be as effective, but it’s much harder to kill everything with it. That peace of mind is worth something.

The algae control aspect is where Excel really shines, though nobody talks about it officially. Many hobbyists use it as a spot treatment for stubborn algae, and it’s remarkably effective at killing brush algae and black beard algae. I’ve used it this way myself, turning off the filter and squirting Excel directly onto affected areas with a syringe.

It works, but it’s technically off-label use. Customer reviews seem generally positive. Amazon shows a 4.6 out of 5 stars rating (Amazon UK), which suggests most people who buy it are satisfied with the results.

That’s not conclusive evidence of effectiveness, but it’s not nothing either. ## The Problems Nobody Talks About Here’s where I start having doubts about Excel, and why I understand the skeptics. The main issue is that it simply doesn’t work for all plants, and Seachem is honest about this. It’s not recommended for Vallisneria species (Seachem), and I’ve seen it damage other sensitive plants too.

My first attempt with Vallisneria spiralis ended with dying leaves within a week of starting Excel. That was an expensive lesson. The chemical reality is also worth considering.

The active ingredient breaks down to compounds including glutaraldehyde, which is commonly used at 2% concentration in disinfectants (CDC). Excel contains much lower concentrations, but it’s still essentially dosing a biocide into your tank. That makes some people uncomfortable, and I understand why.

Cost effectiveness is questionable. At roughly £15 for a 500ml bottle and daily dosing requirements, Excel becomes expensive over time. A basic CO2 setup costs more upfront but works out cheaper per year once you factor in ongoing costs.

If you’re serious about planted tanks, you’ll probably end up with CO2 eventually anyway. The bigger issue is that Excel doesn’t actually solve the fundamental carbon limitation in most planted tanks. It provides some carbon, yes, but not nearly as much as proper CO2 injection.

You’re still limited in what plants you can grow successfully and how fast they’ll grow. It’s a compromise, not a solution. I’ve also noticed that plants seem to become dependent on Excel once you start using it regularly.

Stop dosing for a few days and growth slows noticeably. That suggests it’s providing something the plants are using, but it also means you’re committed to ongoing daily dosing indefinitely. ## The Middle Ground That Makes Sense After eighteen months of using Excel on and off, I’ve reached an uncomfortable conclusion: it works, but not in the way most people expect it to work. Excel isn’t a replacement for CO2 if you want to grow demanding plants or achieve competition-level scapes.

But it is a useful supplement for low to medium tech tanks where you want better plant growth without the complexity of CO2 injection. The key is matching expectations to reality. If you’re trying to grow carpet plants or maintain a proper red coloration in demanding species, Excel alone won’t get you there.

But if you want your Java fern to look healthier and your Anubias to grow a bit faster, it probably will help. I use it now in my main display tank, which runs medium light with no CO2. The plants look better with it than without it, and I haven’t had any fish health issues in over a year of regular dosing.

But I’m also realistic about what it can achieve. It’s a supplement that makes a good tank slightly better, not a miracle product that transforms struggling tanks into aquascaping showcases. The algae control properties make it genuinely useful even if you decide the plant benefits aren’t worth the cost.

Having a bottle on hand for spot treating problem algae is worthwhile, even if you don’t use it for daily dosing. ## The Verdict Excel divides the hobby because it sits in an awkward place between being genuinely useful and being overhyped marketing.

Both sides of the argument have valid points. The people who love it are usually seeing real improvements in their tanks.

The people who dismiss it are usually right that it’s not the revolution in planted tank keeping that some claim it to be. My honest assessment is this: Excel is a decent product that does what it claims to do, but it’s not magic. If you’re running a low-tech planted tank and want to see some improvement without jumping into CO2, it’s worth trying.

Just don’t expect miracles, keep your receipts in case it doesn’t agree with your plants, and be prepared for ongoing costs. The real value might be as a stepping stone. Use Excel to get comfortable with dosing routines and plant care, then move to CO2 when you’re ready for the next level.

Or stick with it if it’s giving you the results you want. The hobby has room for both approaches. See where this placed in our full liquid carbon ranking to understand how it compares to the alternatives.