Tap water contains chlorine, chloramines, copper, phosphates, silicates, and dissolved minerals that drive algae and stress livestock. RO/DI removes 99% of all dissolved solids, giving you the blank canvas your salt mix needs.

How a 4-stage unit works

  1. Sediment filter (5 micron) catches dirt and rust.
  2. Carbon block removes chlorine and chloramines.
  3. RO membrane removes 95–98% of dissolved solids.
  4. DI resin polishes the remaining 2–5% to TDS 0.

What to verify before topping off

A handheld TDS meter should read 0 ppm at the DI output. Replace cartridges when output climbs above 1 ppm.

Related reef reading

Reef tools mentioned in this article

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Water Parameter Tracker

Log every reading. Catch problems before livestock notice.

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