Category: Equipment

Adding CO2 to an aquarium is the biggest single upgrade available to a planted tank, and the one that separates a low-tech setup from a high-tech one. Carbon is among the most essential nutrients aquatic plants take up, and the amount your fish produce does not stretch far once you have fast-growing plants.

Why plants need added carbon

Plants take up carbon as CO2, and it is one of the nutrients they need most. The aquarium’s inhabitants do produce some, but that supply will not suffice where a higher number of fast-growing plants is present. The plants run short long before anything else in the tank does. Aquasabi adds that most deficiency symptoms, yellow leaves included, can come from a carbon shortage, which our yellowing leaves page helps you tell apart.

What happens next is the part worth understanding. Most aquarium plants do not thrive without CO2 fertilisation, but algae does. So a tank short on carbon does not simply grow its plants more slowly. It tilts the balance toward the organisms that cope better with the shortage, which is why black beard algae is so strongly associated with unstable or insufficient CO2. A CO2 shortage is also one of the causes of hair algae.

Do you actually need it?

Not for every tank. Plenty of hardy species grow perfectly well without it, and an entire approach, the Walstad method, is built on going without.

Where it stops being optional is the demanding carpet plants. Tropica rates dwarf baby tears and Glossostigma as high CO2 demand, and says Monte Carlo needs added CO2 to become really compact. Dwarf hairgrass, by contrast, is rated low. The plant ratings chart shows the CO2 rating of every plant on the site.

Measuring it with a drop checker

A drop checker is the standard way to know where you are. It holds an indicator fluid that changes colour according to the CO2 in the water, and it reads as a simple traffic light.

• Blue: too little CO2.
• Green: the level is about right.
• Yellow: too much.

Two things to know before you trust it. The fluid needs several hours to react, so the colour you are looking at reflects the recent past rather than this minute, and you cannot use it to make instant adjustments. And the fluid needs replacing every four to six weeks for the checker to keep working properly. A drop checker filled a year ago is decoration.

A drop checker lags behind

Its colour shows the recent past, not this minute.

Kit

Pressurised systems running from refillable cylinders are the most efficient option. They cost more to set up than the alternatives and then cost very little to run, which is the usual reason people move to one after a while rather than starting there.

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CO₂ questions

Do you need CO2 for a planted tank?

No, not for a low-tech tank of hardy plants. It becomes necessary for plants Tropica rates as high CO2 demand, such as HC Cuba and Glossostigma, and it matters for colour in plants like Alternanthera reineckii, where Tropica calls CO2 material for growth and colour development.

Can CO2 harm fish?

Too much can. That is exactly what the yellow reading on a drop checker is warning you about, and it is the reason to add a checker at the same time as the system rather than afterwards.

Does adding CO2 affect my hardscape?

It can. The carbonic acid that CO2 injection produces dissolves lime deposits faster, so a lime-bearing rock such as Seiryu stone will raise your water hardness more in a CO2-injected tank than in a low-tech one.

Sources: Aquasabi, Refillable CO2 injection system; Aquasabi, Measuring the CO2 level; Tropica, CO2 plant care guide; Tropica, Micranthemum callitrichoides 'Cuba'; Tropica, Glossostigma elatinoides; Tropica, Micranthemum tweediei 'Monte Carlo'; Tropica, Eleocharis acicularis; Tropica, Alternanthera reineckii 'Rosanervig'.

Aquarium plant lighting is the single biggest factor in what you can grow. Match the light to the plants rather than the tank: undemanding ferns and mosses do well in low light, while carpets and red stem plants need considerably more. Get this wrong and no amount of fertiliser rescues it.

How much light your plants need

Tropica, which grows and classifies most of the plants sold in Europe, scales light to the same Easy, Medium and Advanced categories it uses for plant difficulty. Its guidance is that if you have chosen nothing but Easy plants, 10 to 20 lumen (0.25 to 0.5 watts) per litre is adequate. For Medium plants it recommends 20 to 40 lumen (0.5 to 1 watts) per litre, while Advanced plants require more than 40 lumens (1 watt) per litre.

Treat those as bands, not targets. They are useful because they line up with how plants are actually sold, so you can read the difficulty label on a pot and know roughly what you are committing to before you buy.

Shade plants and sun plants

Aquatic plants split fairly neatly into two groups, and the split explains most beginner disappointments.

• Shade plants: ferns and Cryptocoryne grow healthily in low light, and some of them actively do worse under high intensity. Anubias, Java fern and Cryptocoryne wendtii belong here.
• Sun plants: stem plants photosynthesise strongly and grow faster under intense light. Rotala and the red-leaved species sit here, and they need the light to colour properly.

More light is not simply better. Pushing a shade plant under a strong fixture is a reliable way to grow algae on it instead.

Light has to reach the floor

This is where carpet plants catch people out. A carpet only closes if strong light reaches all the way down to the substrate and stays there. Starve it and the plant stretches upward hunting for light, thins out, and never knits together.

Depth matters more than most people expect, which is part of why a wider, shallower tank is easier to plant than a tall one.

Light, CO2 and nutrients move together

Raising light raises demand for everything else. Strong light over a tank without matching CO2 and nutrients does not give you faster plant growth, it gives you algae, because the plants cannot use the light they are being given. Light that is too intense, or left on too long, is one of the causes Aquasabi gives for hair algae. Plants short of nutrients under strong light can also yellow, which our yellowing leaves page covers.

That is the reasoning behind the standard beginner advice to keep light moderate at first. A modest fixture over hardy plants is far more likely to succeed than a powerful one over a sparse new tank. The Walstad method takes this to its logical end and runs deliberately low-tech throughout.

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Lighting questions

How many lumens per litre do aquarium plants need?

Tropica’s guidance is 10 to 20 lumen per litre for Easy plants, 20 to 40 for Medium, and more than 40 for Advanced. Check the difficulty rating on the plants you are buying and work back from that.

Can you have too much light in a planted tank?

Easily. Light drives demand for carbon and nutrients, so a strong fixture over a tank that cannot meet that demand favours algae over plants. Some shade species also grow poorly under high intensity regardless of what else you supply.

What about PAR?

PAR measures the light plants can actually use for photosynthesis, so it describes what reaches a given point in the tank better than a lumen figure does. It is also hard to measure without a meter, which is why lumens per litre and plant difficulty ratings remain the practical way most aquascapers choose a light.

Sources: Tropica, Light guide; Aquasabi, Lighting basics.

Aquascaping tools are long-handled versions of things you already own, and that length is the entire point. Working through 40cm of water with kitchen scissors means a wet sleeve and a disturbed layout. Four items cover almost everything, and you do not need the rest to start.

The four that matter

• Pinsettes (long tweezers): for planting. Grip a stem near its base, push it into the substrate at an angle and release. Trying to plant a carpet with fingers is the fastest way to give up on carpets.
• Scissors: for trimming. Straight blades for stems, curved for cutting a carpet flat without gouging it.
• A spatula or sand flattener: for levelling substrate and shaping slopes before anything goes in.
• An algae scraper: for the front glass. A blade for glass, plastic for acrylic, and never the other way round.

Beyond that, a siphon for water changes is not an aquascaping tool exactly, but it is the one you will use most often.

Straight, curved or angled

Scissors come in all three and the difference is real rather than marketing. Straight blades suit stem plants you are cutting and replanting, which is the constant chore in a Dutch layout. Curved blades follow the contour of a carpet so you can trim it level. Angled ones reach into the back of a deep tank without you leaning over it.

Start with straight. Add curved when you have a carpet worth trimming properly.

Looking after them

Rinse in fresh water and dry them properly after every session. Stainless steel will still spot if it is left wet, and a rusty hinge on a pair of scissors is a tool you will stop reaching for. That is the practical reason to buy decent ones once rather than cheap ones twice.

New to all of this? The beginner’s guide covers what to spend on first, and tools are further down that list than most people expect.

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Questions about tools

Do you really need aquascaping tools?

For a simple low-tech tank, not really. Once you are planting small foreground species or trimming a carpet, long tweezers and proper scissors stop being a luxury and start being the difference between the job taking ten minutes or an hour.

What is the difference between straight and curved scissors?

Straight blades are for cutting stems to replant. Curved blades follow the shape of a carpet so you can trim it flat and even. Most people buy straight first.

Are expensive aquascaping tools worth it?

Up to a point. A decent pair of stainless scissors and tweezers will outlast several cheap sets, mostly because the hinges do not seize. Past that you are paying for finish rather than function.

Aquascaping substrate is more than something to anchor plants in. An active soil changes your water chemistry on purpose, an inert gravel leaves it alone, and which you choose decides whether your plants can feed themselves or need help. Get this right at setup, because changing it later means tearing the tank down.

Active soil versus inert gravel

Aquascaping soils are active substrates. Aquasabi explains that soil works as a cation exchanger: it releases hydrogen ions and removes the calcium and magnesium behind water hardness, lowering pH, total hardness and carbonate hardness. The result is soft, acidic water that suits most tropical fish, shrimp and plants. Soil also stores nutrients and releases them to plant roots when needed.

Inert gravel and sand are water-neutral and supply no nutrients at all. Plants will grow in them, but root feeders have to be fed directly with root tabs pushed into the substrate.

Building it in layers

A nutrient base layer such as ADA Power Sand goes under the soil. Aquasabi says its porous volcanic granules leave gaps that roots grow into, and recommends it for plants that root deeply, naming Cryptocoryne and Echinodorus. A sand cap on top is optional and mostly cosmetic, keeping the soil where you put it and giving a clean front edge.

Slope it deeper at the back. Taller plants root there, and the rise adds depth to the layout in the same way a focal point does.

Which plants care most

• Heavy root feeders: Amazon sword is an Echinodorus, which Aquasabi says actively absorb nutrients through their roots, so give it a nutrient soil or root tabs.
• Rosette plants: Cryptocoryne wendtii roots into the substrate, and Aquasabi says Cryptocoryne need to spread their roots in bacteria-rich substrate.
• Most other plants: Aquasabi notes that nutrient uptake improves for most plants below pH 7, which is where an acidic soil keeps the water.
• Epiphytes: Anubias and Java fern never touch it. They attach to hardscape instead.

The messy start

A fresh nutrient soil releases a lot of ammonium straight after it goes in. Aquasabi’s guide to ADA Amazonia explains that ammonium is not toxic to fish and shrimp in itself, but turns into highly toxic ammonia above pH 7, so it advises planting straight away and adding fish and shrimp two to three weeks after planting. Cloudy water usually comes from granules that dried out or crumbled into powder, and the fix is to remove the cloudy water and refill slowly. ADA also says that once the granules crumble and the substrate becomes less permeable, blue-green algae may develop in it, and the answer then is to rebuild the substrate. The Walstad method accepts a similarly rough start with ordinary soil under gravel.

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Substrate questions

Do you need aquasoil for a planted tank?

No, but it makes life easier. Plants grow in inert gravel provided root feeders get root tabs. An active soil stores nutrients for the roots and softens the water, which Aquasabi says suits most tropical fish, shrimp and plants.

Can you put sand on top of aquasoil?

Yes, as a cap. It holds the soil in place and gives a tidy front edge. Keep it shallow so plant roots can still reach the nutrients underneath.

Why is my new tank cloudy after adding soil?

Usually because the soil granules dried out or crumbled into powder. Aquasabi’s advice for ADA Amazonia is to remove the cloudy water and pour new water in slowly. New soil also releases ammonium at first, so wait two to three weeks after planting before adding fish or shrimp.

Sources: Aquasabi, Soil; Aquasabi, ADA Power Sand; Aquasabi, ADA Substrate Fertilizers; Aquasabi, ADA Aqua Soil Amazonia.