RO/DI Water for Reef Tanks: Why Tap Water Will Crash Your Reef

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.