RO/DI Water for Aquariums — Why It Matters & How to Use It

Tap water contains chlorine, chloramine, heavy metals, phosphates, silicates, and other contaminants that wreak havoc in sensitive aquariums — especially reef tanks. Reverse Osmosis / Deionization (RO/DI) filtration removes virtually all of these, giving you a pure starting point to build the perfect water chemistry.

What Does RO/DI Remove?

• Chlorine and chloramine
• Heavy metals (copper, lead, zinc)
• Phosphates (algae fuel)
• Silicates (cause diatom blooms)
• Nitrates and nitrites
• Most dissolved solids

A quality RO/DI system produces water with a TDS (Total Dissolved Solids) reading of 0–5 ppm — essentially pure water.

Do You Need RO/DI?

• Reef tanks: Yes, absolutely. Saltwater chemistry is precise; tap water inconsistencies cause problems.
• Planted freshwater tanks: Recommended if your tap water is very hard or has high TDS.
• Fish-only freshwater: Often not necessary if tap water is conditioned and stable.

How to Use RO/DI Water

RO/DI water has a TDS of ~0, meaning it has no buffering capacity. You must remineralize it before use:

• Freshwater: Add a remineralizer like Seachem Equilibrium to raise GH/KH to target levels
• Saltwater/Reef: Mix with quality reef salt to reach salinity of 1.025 sg (35 ppt)

Storing RO/DI Water

• Use food-grade containers or dedicated RODI storage bins
• Keep containers covered and dark to prevent algae and contamination
• Change stored water within 2–3 days, or aerate continuously

Shop RO/DI Systems

We carry a full range of RO/DI units — from compact 4-stage systems to high-capacity reef systems — in our Aquarium Supplies collection. Browse AquaticLife systems available in store and online.