Osmolator and Water Container

Osmolator and Water Reservoir, Daily Salinity Stability

The osmolator (ATO) automatically compensates for evaporation by adding osmosis water from a reservoir, which stabilizes salinity and prevents daily variations. The key advantage is consistency: a level sensor triggers a small dosing pump, often with an anti-overfill safety feature to minimize risks. This stability is particularly useful in reef aquariums, where corals react quickly to imbalances.

Historically, Tunze is often cited as a pioneer with the Osmolator introduced in 1985, a milestone in the democratization of "plug & play" ATO systems. Source

The water reservoir complements the system: it provides autonomy (weekends, holidays) and allows for sizing the safety volume. A good practice is to choose a food-grade container, covered, easy to refill, and suitable for the tank's evaporation consumption.