Do you need CO2? Low-tech vs high-tech planted tanks

"Do I need CO2?" is the biggest fork in the planted-tank road. The honest answer: no — but it changes what you can grow.

Low-tech (no CO2):

• Relies on the small amount of CO2 fish and bacteria produce.
• Pair with lower light and a modest photoperiod — too much light without CO2 just feeds algae.
• Grows a huge range of hardy plants: java fern, anubias, cryptocoryne, java moss, vallisneria, many stems slowly.
• Cheap, low-maintenance, forgiving. A great place to start.

High-tech (injected CO2):

• Pressurized CO2 lets plants use higher light and nutrients, so they grow faster — and you can keep demanding carpets and red plants.
• Requires more gear (CO2 system, diffuser, drop checker), more dosing, more trimming, and getting it wrong can harm fish.
• More work and cost, but the lush aquascape look usually needs it.

The trap is buying high light with no CO2 — that combination grows algae faster than plants. Match your light to your carbon.

Your turn: low-tech or high-tech, and what are you trying to grow? If algae is winning, post your light, photoperiod, and dosing — that trio usually reveals the problem.