The H2Ocean Compact Automatic Top-Up Unit is a streamlined, reliable ATO system designed for hobbyists who want accurate water-level maintenance without the bulk of larger controllers. Using a compact solid-state optical sensor and intelligent refill logic, it ensures stable water levels and prevents salinity swings caused by evaporation.

This unit is ideal for smaller aquariums, nano reefs, sumps, and AIO systems where space is limited but precise top-off control is essential. Installation is fast and simple, with an included mounting clip, pump, and all required tubing.

For aquariums where additional safeguards are required — including multi-sensor redundancy and a built-in leak alarm — consider upgrading to the H2Ocean Advanced Automatic Top-Up Unit , which offers enhanced protection for larger or higher-value systems.

Key Features

• Compact optical water-level sensor for accurate detection
• Smart refill logic to prevent over-filling
• Quiet, efficient top-off pump included
• Ideal for nano tanks, AIO aquariums, and compact sumps
• Quick installation with mounting clip and tubing
• Maintains salinity stability by compensating for evaporation

For manuals, spare parts lists, and instructional videos, please visit the official D-D product page:
View the official D-D product page