RO vs RODI - Whats the difference?
If you're serious about maintaining a healthy, vibrant aquarium—especially a reef tank—then you’ve probably heard of RO and RODI water. While both are excellent filtration options, understanding the difference between them can have a significant impact on your tank's long-term success.
In this post, we’ll break down what RO and RODI water are, how they’re made, and why choosing the right one matters for your aquarium.
What Is RO Water?
Reverse Osmosis (RO) is a water purification process that uses a semi-permeable membrane to remove contaminants from tap water. During this process, water is pushed through the membrane under pressure, leaving behind impurities such as:
Chlorine and chloramine
Heavy metals (like lead and copper)
Dirt, sediment, and some bacteria
Dissolved solids (TDS)
Certain organic compounds
RO systems can remove up to 95–99% of these impurities, making RO water a huge upgrade from untreated tap water. It provides a clean, neutral base that can be further customized with buffers and additives depending on the needs of your aquarium.
However, it’s important to note that RO does not remove everything—some small ions, like nitrates or phosphates, can still slip through the membrane.
What Is RODI Water?
Reverse Osmosis Deionization (RODI) water takes purification one step further. After going through the RO system, the water passes through a deionization (DI) resin filter, which uses ion exchange to strip away any remaining charged particles, including:
Nitrates
Phosphates
Silicates
Calcium, magnesium, and other ions
This final stage of filtration results in ultra-pure water with 0 TDS (Total Dissolved Solids). That’s why RODI water is considered the gold standard for saltwater and reef aquariums—where even trace impurities can lead to problems like algae blooms, coral stress, or unwanted chemical fluctuations.
Why It Matters for Your Aquarium
The type of water you use sets the foundation for everything that happens in your aquarium. Here’s why RODI water is often the best choice:
✅ Eliminates nuisance nutrients: No nitrates or phosphates means a lower risk of algae problems.
✅ Consistent water chemistry: You’re starting with a blank slate, so you can precisely control what goes into your tank.
✅ Protects sensitive marine life: Corals and invertebrates thrive in ultra-clean, stable environments.
✅ Improves clarity and cleanliness: Fewer impurities lead to clearer, healthier water overall.
In short, RODI water gives you more control, more stability, and better long-term results—especially in delicate reef systems.
Which Should You Use?
Freshwater aquariums: RO water is usually sufficient, especially if you’re re-mineralizing the water to match your fish's needs.
Saltwater and reef aquariums: RODI water is the best choice. The extra purification ensures there are no hidden contaminants that could harm your corals or disrupt your tank’s balance.
Final Thoughts
While RO water is a great first step, RODI water provides the cleanest, most stable foundation for your aquarium. Whether you're keeping freshwater fish or building a full-scale reef tank, using the right type of purified water can make all the difference.
At Pure RO Systems, we specialize in RODI water filters built specifically for aquarium hobbyists. Our systems are designed for performance, reliability, and ease of use—helping you create the ideal environment for your aquatic life.
Explore our RODI filter systems today and take your aquarium to the next level!
