Now you can add a Trigger Automatic Top Off Reservoir to go with your Crystal, Sapphire, Ruby, Emerald, or Amethyst sump. Constructed with the same amazing quality, the Trigger ATOs are built to last just like the sumps. ATOs are used to hold RO/DI water to replenish your tank in the event of water evaporation. Please remember to fill your ATO reservoir with freshwater only to keep your salinity balanced. For any questions, you can reach out to us on our Contact Us page.