Aquatic plants, also referred to as hydrophytes,[1] are vascular plants and non-vascular plants[2] that have adapted to live in aquatic environments (saltwater or freshwater).Aquatic plants require special adaptations for prolonged inundation in water, and for floating at the water surface.
Does KH matter in a planted aquarium ? What is a good level of KH to have? Is it necessary to buffer the tank from pH crashes?When it is said in the hobby that an aquatic plant requires "soft water", this generally means that the plant requires low KH, not low GH.
Tank Requirements and Water Parameters.Oxygenation: Just like other aquatic plants, Marimo uses up CO2 and provides oxygen in the tank as a result of the photosynthesis process, and this is needed by aquatic animals for survival.

CO2 and plants, CO2 injection, benefits of CO2 in Your Tank, vibrant aquatic plants, faster plant growth, red plant colors, high tech plants, CO2 for aquascaping.
It is required for respiration and growth by all aquatic plants, used in a process called photosynthesis. Plants require a constant supply of CO2 during the light hours, otherwise they suffer. They combine the CO2 with water and light energy to produce oxygen and sugars to enable growth.

Planted Tanks: PAR Requirements by Plant Type. Low tech / low light plants (anubias, java fern, cryptocorynes, mosses): 2050 PAR at substrate level. No CO2 required. Nearly any aquarium LED achieves this.