Ryznar Stability Index Calculator

The Ryznar Stability Index (RSI) predicts whether water will deposit scale (calcium carbonate buildup) or corrode pipes — a critical check for cooling systems, boilers, and water treatment. Enter your water's pH, temperature, calcium, total alkalinity (HCO3), and total dissolved solids (TDS) to calculate the RSI score and see your water's tendency toward scaling or corrosion. Secondary outputs include the Langelier Saturation Index (LSI) and pH at Saturation (pHs).

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Results

Ryznar Stability Index (RSI)

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Langelier Saturation Index (LSI)

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pH at Saturation (pHs)

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Water Tendency

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Frequently Asked Questions

What is the Ryznar Stability Index (RSI)?

The Ryznar Stability Index is a water quality parameter used to predict the corrosion and scaling potential of water. It's calculated as RSI = 2(pHs) - pH, where pHs is the pH at saturation.

How do I interpret RSI values?

RSI < 6: High scaling potential; RSI 6-7: Stable water with slight scale tendency; RSI 7-8: Slight corrosion tendency; RSI > 8: High corrosion potential with mild steel corrosion problems.

What's the difference between RSI and LSI?

LSI (Langelier Saturation Index) indicates calcium carbonate saturation, while RSI attempts to correlate scale thickness observed in water systems. RSI provides better correlation with actual scaling behavior in municipal systems.

What water parameters do I need to calculate RSI?

You need pH, temperature, calcium concentration, total alkalinity (bicarbonate), and total dissolved solids (TDS) to accurately calculate the Ryznar Stability Index.

When should I be concerned about my RSI value?

Values below 6 indicate high scaling potential requiring treatment, while values above 8 suggest corrosive water that may damage pipes and equipment. Target RSI values between 6-7 for optimal water stability.

How can I improve my water's RSI?

For scaling water (RSI < 6), consider pH reduction or chemical treatment. For corrosive water (RSI > 8), pH adjustment, alkalinity increase, or corrosion inhibitors may be needed.

Is RSI applicable to all water systems?

RSI was developed for municipal water systems and works best for calcium carbonate systems. It may be less accurate for industrial processes or waters with unusual chemistry.