Caridina shrimp, such as Crystal Red Shrimp (CRS), Crystal Black Shrimp (CBS), and other varieties, are typically kept in freshwater aquariums. The substrate required for them can vary depending on your setup and preferences, but generally, a fine-grained substrate is recommended. Here are some options:

• Inert Substrate: Many hobbyists prefer inert substrates like aquarium sand or fine gravel. These substrates do not alter water parameters, which is crucial for maintaining stable conditions in the shrimp tank.
• Active Substrate: Some aquarists opt for active substrates like specialized shrimp substrates. These substrates often contain buffering properties that can help maintain stable pH and hardness levels, which can be beneficial for Caridina shrimp that prefer slightly acidic to neutral water conditions.
• Aquasoil: Another popular option is aquasoil, which is a type of planted tank substrate. Aquasoil not only provides a good environment for plants but also helps maintain stable water parameters favored by Caridina shrimp.
• Sandy Substrate: Some shrimp keepers prefer sandy substrates, as they mimic the natural environment of many Caridina species. Sands like ADA Amazonia or CaribSea Super Naturals can be good choices.
• Shrimp-Specific Substrate: There are substrates specifically marketed for shrimp tanks. These often have added minerals and nutrients beneficial for shrimp and plant growth.
  
  Regardless of the substrate you choose, it’s essential to ensure that it’s thoroughly rinsed before adding it to the tank to remove any dust or debris. Additionally, make sure the substrate layer is not too deep, as excess substrate depth can lead to anaerobic pockets forming, which may cause issues with water quality. Aim for a depth of around 1-2 inches (2.5-5 cm) for most substrates.