Fixing a ato

[Perthegallon]

Hello so I have a ato on my waterbox marine the display is about 50 gallons and sump 20 I have a issue with the ato it seems to detect the water being lowered when the water level goes down to far and then starts to beep and stop filling thinking it will over flow if it continues this is my sump any help would be appreciated

 

[homer1475]

What ATO are you using?