Tsunami AT-1 Auto Top-Off System ATO. The Tsunami AT1 uses a powerhead or pump (user supplied) to keep a constant level in a sump. When the water level in the sump drops 1", the AT1 will turn on the reservoir pump and turn it off after the sump fills up 1". Features: - Prevents main pump from running dry. - Holds sump levels constant. - Reduces salinity fluctuations. - Includes water level sensor. - Circuitry designed to UL specifications.