Aquarium Auto Top Off Self-Leveling Controllers automatically replenish water to a sump or tank. Dosing pumps automatically and slowly replenish liquid supplements. Useful Articles: Why Use A Dosing Pump? I A Simple Guide To Auto Top Offs.

From our A Simple Guide To Aquarium Auto Top-Offs Article:

Automatic aquarium top-off systems are the best way to create a consistent water level in your aquarium. A consistent water level will stabilize your water parameters, providing a stable environment for your animals. An aquarium auto top-off will also save you time and make it easy to maintain your water level during a vacation. Added benefits include better protein skimmer performance and supplement dosing.

Here is a detailed list of the benefits of an auto top-off:
Increased Stability – Maintaining water levels is critical to maintaining your water parameters. When your water evaporates it causes many water parameters to change. Simply put, when the water evaporates there is less water and the same amount of everything else. This means that when water evaporates your calcium, ammonia, nitrate, phosphate, and salinity concentrations all increase. Adding an auto top-off can reduce these changes and provide a more stable environment for your animals. . . .continued