How to Set Up a Planted Aquarium Without CO2
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Here is how to setup a planted aquarium without CO2: build a low-energy tank: keep the lighting modest, use a nutritious substrate at least 2 inches deep, choose easy plants, and add a liquid fertiliser on a steady schedule. Low-energy tanks need less fertiliser and fewer water changes than high-energy ones, and they do not need CO2 equipment. This guide walks through each step in order and explains why brighter light usually causes more trouble than it solves. It also covers what the sources do not cover, so you know where to check a plant’s own care notes.
Quick answer
- Use the stock light from your tank kit; do not upgrade to something brighter.
- Run the light on a timer for a fixed eight hours a day.
- Use a nutritious substrate, at least 5 cm (2 inches) deep.
- Pick easy plants and dose a quality liquid fertiliser weekly.
Step 1: Decide on a low-energy tank
Swell UK rates tanks as high, medium or low energy, mostly based on lighting. More light raises plant metabolism and the demand for CO2 and fertiliser, which is exactly what you are avoiding. A low-energy tank stays balanced with ordinary lighting, which is why it works without injected CO2. Expect slower growth. That is not a failure; it is how this style behaves.
Step 2: Keep the lighting modest
Standard lighting from a tank kit is adequate, according to the guide. Resist adding brighter light. Bright light without matching nutrients leads to algae. Put the light on a plug-in timer and set a fixed eight hours a day. Consistency matters more than cleverness here, and a timer removes the guesswork. Our guide on a betta light timer for day and night shows how to set one up, and a comparison of planted aquarium lights is worth reading if you later want to step up your lighting.
Step 3: Build the substrate
Use a nutritious substrate, as you would with CO2, because the roots do much of the feeding. The guide lists three approaches:
- Aquatic soil on its own.
- A layer of substrate fertiliser under the gravel.
- Fertiliser balls pushed into the gravel.
Aim for a depth of at least 5 cm (2 inches); deeper is better. Hide the layers under a cap if you use fertiliser below gravel so the nutrients stay put. If you are choosing between sand and gravel for the top layer, our substrate guide for bettas explains the trade-offs.
Step 4: Choose filtration and flow
Flow does not need to be high. The guide says an internal canister filter is sufficient, and an external canister in the cabinet underneath is better. A filter with a built-in heater keeps the heater out of sight. If you keep a betta, remember that strong currents can bother long-finned fish, so look at a betta-size heater and a gentle filter together.
Step 5: Pick plants that suit a no-CO2 tank
Choose plants from the easy range, as these give the best chance of success. Swell UK lists these genera as suitable:
| Group | Genera listed |
|---|---|
| Attach to wood or rock | Anubias, Bucephalandra, Microsorum |
| Rooted | Cryptocoryne, Echinodorus, Sagittaria, Vallisneria |
| Stem and bushy | Bacopa, Ceratophyllum, Hygrophila, Lobelia, Ludwigia, Staurogyne |
The grouping in the table is a convenience; the source simply lists the genera. Buy plants that are strong, healthy and free of algae. Another guide from a hobby retailer mentions species such as Hygrophila polysperma and Marsilea hirsuta as tolerant of low CO2, and says some carpet plants grow slowly without CO2.
Step 6: Feed the plants
Plants still need a complete range of nutrients, even at lower uptake rates, so use a quality liquid fertiliser. Dose weekly after a water change, or divide the weekly recommended amount by seven and dose daily. Follow the bottle’s directions for the amount; the source does not give a number.
Step 7: Plant, fill and be patient
Plant first, then fill slowly so the substrate does not shift. Trim yellowing leaves and keep an eye out for algae. Slow growth means trimming is a light job. Before adding fish, cycle the tank. Our Aqueon versus Tetra aquarium kit comparison shows what comes in common starter kits, including stock lights.
A simple weekly routine
A routine keeps a low-energy tank steady, and the steps below only use points from the sources. First, confirm the light timer is still set to eight hours. Second, do a water change and then dose the liquid fertiliser, since Swell UK says to dose weekly after a water change. Third, trim any yellowing or algae-covered leaves, because the guide stresses buying and keeping plants that are healthy and free of algae. Fourth, look at the substrate: if plants are rooted in a nutritious layer, roots should stay covered. Finally, watch the plants themselves. Pale new growth, holes or sudden algae are signs that light, nutrients or both are out of balance, and the fix in a low-energy tank is almost always to reduce light or adjust the fertiliser, not to add equipment.
Why the no-CO2 approach is forgiving
In a tank without CO2, plants grow slowly, so nutrient demand is low and mistakes show up gradually rather than overnight. That is why the guide recommends keeping the stock lighting. With less light, plants need less CO2 and fertiliser, so the tank stays in balance without extra equipment. Buceplant describes the same idea from another angle: light is the main variable, and too much light without enough carbon leads directly to algae, while too little makes plants stagnate. The sensible target is therefore a middle path using the light that came with the tank, easy plants, and regular but light care. If you later feel the urge to upgrade, treat it as a new project that will also change fertiliser and maintenance needs, not as a simple swap.
What the sources do not cover
- Fish stocking levels.
- A fixed water change schedule; the guide says only that low-energy tanks need fewer changes.
- How long to wait before adding plants or fish.
For those points, follow the care sheet for the fish you keep and ask a vet or experienced local aquarium store if you are unsure.
Common mistakes
- Adding brighter light. It raises nutrient and CO2 demand and invites algae.
- Thin substrate. Roots need depth; stay at 2 inches or more.
- Skipping fertiliser. Lower uptake is not zero uptake.
- Hard-to-grow plants. Start from the easy list.
FAQ
Can I really grow plants without CO2?
Yes. A low-energy tank with modest light and easy plants is built for exactly that.
How long should the light stay on?
Swell UK recommends a fixed eight hours a day on a plug-in timer.
Do I still need fertiliser?
Yes. Plants still need a full range of nutrients; use a quality liquid fertiliser weekly or split the dose daily.
Which plants should beginners choose?
Anubias, Cryptocoryne, Vallisneria and the other easy genera listed above.
Is a bigger light better?
No, not for a no-CO2 tank. More light increases plant metabolism and algae risk.
Bottom line
Keep the light modest and timed, build a deep nutritious substrate, plant easy species, and dose fertiliser steadily. That is the whole recipe for a planted tank without CO2.
