Hydro-link sponges can be re-used as long as they don't get damaged, which is indicated with:
1. Sponges start to fall apart.
2. They change color.
To prevent this from happening, make sure to remove them from the saline solution if they won't be used. Also, try to prevent the Hydro-link from being scratched by any parts of the plastic holder and the electrode base.
According to the internal tests, Hydro-link sponges can be reused at least 20 times. This is a consumable part so if the sponge is obviously damaged, it's recommended to replace it with a new one.