Neptune Systems ATK V2 Auto Top Off KitA Complete, Simple, & Standalone ATO! If you want a safe ATO system, the Neptune System ATK v2 uses a mixture of optical eyes and a float valve to ensure your tanks water level stays the same while preventing overfills. With the ATK v2 you do not need an Apex Controller since it can be run 100% standalone, however with the addition of an Apex Controller additional features can be unlocked and more accessories can be added to the included FMM module.