7 Essential RO/DI Tips for a Thriving Saltwater Aquarium
Maintaining a healthy, vibrant saltwater aquarium starts with something many beginners overlook - the quality of your water. Using an RO/DI (Reverse Osmosis/Deionization) system is one of the best ways to ensure your reef stays clean, stable, and free from harmful contaminants. But just owning an RO/DI unit isn’t enough - you have to use it correctly!
This article breaks down 7 common RO/DI mistakes and how to avoid them so your saltwater tank can thrive.
1. Not Using an RO/DI System to Filter Tap Water
Tap water might be fine for drinking, but it’s packed with chlorine, chloramines, silicates, nitrates, and heavy metals—all of which can spell disaster in a reef tank. These contaminants fuel algae growth, stress corals, and disrupt water chemistry.
Always start with purified RO/DI water. It gives you complete control over what goes into your tank and sets the foundation for long-term success.
2. Not Using an Auto Shut Off Valve to Stop Water Production Automatically
Leaving your RO/DI system running without an auto shut off (ASO) valve can waste water and risk flooding your floor or mixing station. An ASO valve stops the flow once your storage container is full, preventing overflows.
Invest in an auto shut-off valve and pair it with a float valve or electronic sensor - it’ll save water, prevent spills, and give you peace of mind.
3. Not Changing Your Filters on Time
Clogged or exhausted filters reduce system efficiency and allow contaminants to pass through. Pre-filters like sediment and carbon cartridges should be replaced regularly to protect the RO membrane and keep water quality high.
Stick to a maintenance schedule and monitor filter life. Don’t wait until your water quality drops to take action.
- Sediment Filter: Every 3-6 months. When you see a pressure drop going into your RO Membrane via the inline pressure gauge, it's time to swap out the sediment filter. Shop Sediment Filters >>
- Carbon Block: Every 3-6 months. Test for the presence of Chlorine and Chloramines using Total Chlorine Test Strips in your RO System's wastewater. If chlorine shows up, swap out your carbon filter. Shop Carbon Block Filters >>
- RO Membrane: Every 1-3 years, pending water quality and usage. Monitor your RO Membrane rejection rate using an inline or handheld TDS meter. When product water TDS starts to climb, your RO Membrane should be changed out. Shop RO Membranes >>
- DI Resin: Approx. once a year, pending water quality and usage. Monitor TDS of your product water and use color-changing DI resin to indicate when it is time to swap out the DI Resin. Shop DI Resin & Filters >>
4. Ignoring Water Pressure
Your RO system is pressure-sensitive. Low water pressure (<50 psi) drastically reduces output and filtration efficiency, while high pressure can damage components. Most systems operate best between 60–80 psi.
Use a pressure gauge and, if needed, install a booster pump to keep your system in the optimal range.
5. Not Using Your TDS Meter to Monitor System Performance
TDS (Total Dissolved Solids) meters tell you how pure your water is. If your TDS starts to creep up, it’s a clear sign your filters or membrane need attention. Ignoring TDS levels can lead to poor water and unhappy corals.
Check your TDS regularly—before and after filtration. Aim for 0 TDS coming out of the DI resin for reef-ready water.
6. Not Flushing Your RO Membrane
RO membranes collect debris and minerals over time. Flushing the membrane regularly helps remove buildup, prolongs membrane life, and maintains optimal flow and rejection rates.
Use a flush kit to clean your membrane periodically, especially after large batches or long idle periods.
7. Not Using the Right Container to Store Your RO/DI Filtered Water
Storing RO/DI water in containers that leach chemicals or harbor bacteria can undo all your filtration efforts. Avoid reused food-grade containers not intended for long-term water storage.
Use dedicated, food-safe containers (HDPE is best) with lids to keep your water clean, secure, and contamination-free.
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