The Red Sea ReefCan Reservoirs (18 and 40 liters) have been specifically designed to meet the needs of hobbyists, capable of supplying sufficient water for the auto top-off (ATO) of a 200-liter or 500-liter aquarium for about a week. They fit inside the technical cabinet or behind the tank, can be refilled without the need to remove the container and disconnect its hoses and cables, and feature a transparent plastic housing with an integrated water scale, allowing you to see how much RO water is left.
ReefCans utilize the often-unused dimension in your system's cabinet, namely height, resulting in more RO water with less valuable floor space.