The LSI equation needs your Carbonate Alkalinity, which requires a correction against Total Alkalinity (TA) based on Cyanuric acid (CYA) at a given pH. The Orenda calculator makes this correction automatically for you.

Input your Total Alkalinity into the calculator. As you adjust your CYA level, the LSI will change accordingly.

The LSI equation needs your Total Dissolved Solids (TDS) level. TDS includes salt. We have this named "TDS/Salt" for two reasons:

• Many people forget about salt, or do not associate salinity with TDS. It's very important to include it for an accurate LSI calculation.
• This is also a dosing calculator. So if you need to add salt to your pool, this will tell you how much you need for your pool.

Input your Total Dissolved Solids, including salt, into the calculator. If you do not have a TDS meter, you can estimate TDS by adding salt + calcium + total alkalinity + CYA. But a TDS meter is more accurate.

We have included the pH ceiling on the Orenda Calculator to show you how high your pH will naturally rise.

The more dissolved carbon dioxide (CO₂) in the water, the lower the pH, and vice versa:
↑CO₂ dissolved = ↓pH
↓CO₂ dissolved = ↑pH

Learn more about CO₂ and pH here.

Henry's Law of physics explains why CO₂ must off-gas from a swimming pool to equalize with the air above the pool. The same exact physics applies to carbonated drinks that eventually go flat.

The precise point at which CO₂ is in equilibrium with CO₂ above the water is known as pH(eq), or as we at Orenda call it, the pH ceiling. This is the moment your pool is "flat". It is the highest your pH can naturally rise at a given carbonate alkalinity and temperature.

Factors such as auto-covers, acid feeders and trichlor feeders can suppress pH, but otherwise, the pH is heading toward the pH ceiling, thanks to physics.

Warning: pH and alkalinity adjustments/dosing become distorted and inaccurate above 150 ppm TA. If you currently have over 150 ppm TA, reduce it no more than 20 ppm at a time with diluted acid until your desired level.

If you're trying to raise TA over 150, this too will cause issues like a rapidly-rising pH (elevated pH Ceiling) and an LSI that will likely lead to scale formation. It will also increase the amount of acid needed for pH corrections.

Learn more here.

Error: The numbers you have inputted for CYA and Alkalinity are not possible. Your Cyanurate Alkalinity is higher than what you have inputted for Total Alkalinity. Double check your chemistry readings and try again.

If your CYA is over 100 ppm, we recommend diluting water to reduce it. The higher your CYA, the slower your chlorine, and that can pose health and safety risks to bathers. We at Orenda recommend less than 50 ppm CYA.

Learn more here.

Your carbonate alkalinity is below zero. Either your total alkalinity is too low, or your CYA and/or Borate levels are too high. Double check your inputs. If your imputs are correct, either raise total alkalinity, or drain and dilute your pool to reduce CYA and/or Borates.

Learn more about carbonate alkalinity.

The Langelier Saturation Index (LSI) is the objective measurement of water balance, based on the saturation of calcium carbonate (CaCO₃). Too much (high LSI) leads to scale, and too little (low LSI) leads to etching damage. Aim to keep your water from becoming RED or PURPLE on this calculator all year long.

Color Legend:

• LSI ≥ 0.3: Scale forming
• 0.00 to 0.30: Ideal balance
• -0.30 to -0.01: Acceptable balance
• LSI < -0.3: Etching/Aggressive

While Orenda does not endorse the use of borates in swimming pools, many find borates helpful for maintaining water balance. Specifically, borates are used for slowing the natural rise in pH.

Borate is a buffer against a rise in pH, much like carbonate alkalinity is a buffer against a reduction in pH.

Like CYA, borates contribute to Total Alkalinity (TA), and therefore must also be deducted when calculating the water's carbonate alkalinity (or corrected alkalinity), which is required for the LSI equation.

The Orenda Calculator makes all of these corrections for you automatically. Just input your borate level and the other factors, and the LSI will adjust on the calculator in real-time.

Be aware: For health and safety reasons, never exceed 50 ppm borate in your water. Experts recommend 30-50 ppm. Learn more about borate toxicity here.

Learn more about borates here.

This acid dose is the total amount of acid required to achieve your desired alkalinity. We strongly advise against reducing TA more than 20 ppm at a time.

If you're adding too much acid at once, it can cause an LSI violation and damage to your pool surface and equipment. Take your time with alkalinity; it is not a race! Reduce alkalinity over several treatments with diluted acid. The more dilution, the better. When in doubt, use less acid and dilute it a minimum of 10:1 in buckets of water.

When reducing alkalinity, give your pool time to aerate and off-gas CO₂ so the pH can rise. If you have an automatic cover, leave it open during this process, otherwise pH will be suppressed and problems can occur.

Learn how to properly lower alkalinity here.