Supplements for Osmosis Water
Supplements for RO water in a marine aquarium are mainly used in top-off/ATO to keep pH, KH, and calcium stable when reactors or dosing pumps are not used. The most common solution is kalkwasser (calcium hydroxide).
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When to use them: reef tanks with moderate Ca/KH consumption, setups without a calcium reactor or 2/3 part systems. They are usually not needed in fish-only tanks.
Preparation & use: dissolve the supplement in RO water in a separate container, stir, let it settle, and use only the clear solution via ATO. Never add salt to the top-off water.
Checks & safety: monitor pH, KH, Ca; gradually increase the concentration to avoid precipitation and pH spikes. Do not mix other non-expressly compatible products in the ATO reservoir.
Alternative: if consumption is high, consider dosing pumps (2/3 parts) or a calcium reactor for finer control of the ionic balance.