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Planted aquariums

Planted tank basics: substrate, lighting, and CO2

You can start a planted freshwater tank without injected CO2. Choose plants that suit your light, put them in the right place and adjust nutrients from how they grow.

2 min readUpdated September 27, 2026By FishicianPublished August 27, 2026How we source

The short answer

  • Balance light, carbon and nutrients. More light raises plant demand for carbon and nutrients; increase it only when growth supports the change.
  • Plant for the way it grows. Rooted plants go in substrate; Anubias and java fern can attach to wood or rock with their rhizomes exposed.
  • Start with moderate light, not maximum output for a long day. Increase gradually.
  • CO2 injection is optional. Low-tech and high-tech both work; they suit different plants and effort.
  • If fish gasp, act immediately. With injected CO2, stop its delivery safely and increase aeration while checking the cause.
An aquascaper places a small Anubias plant with long tweezers
Planting Anubias with aquarium tweezers. Plant placement and species choice shape a planted tank.Photo: An Aquascapist Planting Aquatic Plant Anubias Petite with Tweezers in an Aquarium — Abhik.Mazumdar.73 · CC BY 4.0. Resized for display.
Low-tech or high-tech
Without injected CO2
  • Choose suitable easy plants
  • Moderate light
  • Match nutrients to growth
  • A simpler starting point
With injected CO2
  • More equipment and monitoring
  • Can support demanding plants
  • Balance light and nutrients
  • Protect gas exchange and fish

Choose plants, then place them

Check each plant's light, size and CO2 requirements before buying. Anubias, java fern and suitable Cryptocoryne varieties offer useful starting choices; a group name alone does not guarantee identical care.

  • On wood or rock: attach Anubias and java fern without burying the rhizome, the horizontal stem from which leaves and roots grow.
  • In the substrate: plant roots of rosette plants such as Cryptocoryne according to their planting instructions.
  • Nutrients: rooted plants can use a suitable nutrient substrate or root tabs; attached plants need nutrients available in the water.

Follow the substrate's directions for rinsing or capping. These are product-specific, not a rule for every planted substrate. See substrate and hardscape.

Set a manageable light routine

Start with moderate light suited to the chosen plants and a consistent day/night cycle. Wattage measures power use, not the light reaching each leaf; tank depth and shading matter.

Do not raise brightness and extend the day together to chase faster growth. Watch new growth and algae, change one input at a time, and use the lighting guide to refine the routine.

Feed for the plants you have

Plants need carbon and mineral nutrients, including nitrogen, phosphorus, potassium and trace elements. What to add depends on plant demand, the substrate and nutrients already in the water.

Follow the fertilizer's starting dose and observe growth before adjusting. Poor growth has several causes; algae alone does not identify a deficiency. More light or more fertilizer is not automatically the next step.

If you add CO2

Suitable easy plants can grow using the CO2 already available in the tank. Injection expands your choices but adds equipment and monitoring.

  • Follow the equipment's operating and night-control instructions. Maintain gas exchange; do not seal a gas-producing system to stop its flow.
  • A drop checker responds slowly and cannot warn instantly of excess CO2. Watch the animals as well as the indicator.
  • If fish gasp or deteriorate, stop CO2 delivery safely and increase aeration immediately. Check equipment and water quality; seek aquatic-veterinary help if distress is severe or persists.
What changes after lights-out?

In light, photosynthesis uses CO2 and produces oxygen. At night it stops, while respiration continues to use oxygen and release CO2. Injection and gas exchange also affect levels.

CO2 changes pH; it does not by itself consume total alkalinity. See water parameters.

Sources

Each source is listed with the part of this guide it supports.