What is Sodium Carbonate Peroxyhydrate primarily used for?

Sodium Carbonate Peroxyhydrate is primarily used as an algaecide because it releases hydrogen peroxide when dissolved in water. This release of hydrogen peroxide is effective at controlling algae growth by disrupting the cellular structure of the algae, ultimately leading to their death. It acts by oxidizing the organic matter that is present in the water, making it particularly useful in managing algal blooms that can harm aquatic ecosystems.

While the other options mention benefits related to aquatic environments, they do not align with the specific use of Sodium Carbonate Peroxyhydrate. Enhancing fish habitat and increasing dissolved oxygen are important considerations in aquatic management but are not functions of this compound. Additionally, reducing water hardness is not a property or purpose of Sodium Carbonate Peroxyhydrate, as it does not directly impact the calcium and magnesium ions that contribute to water hardness. Therefore, the correct association with Sodium Carbonate Peroxyhydrate is its role as an algaecide.