Your service report includes chemical readings from each visit. Based on standards from the Pool & Hot Tub Alliance (PHTA) and the CDC's Model Aquatic Health Code, this guide explains what each parameter measures, why it matters, and what the target range is for pools in the Oak Island area. Not every reading appears on every report - some are tested weekly, others monthly or as conditions require.
See what your report looks like:
What Does Each Chemical Reading on My Service Report Mean?
Temperature
Pool temperature directly affects chemical reaction rates. Warmer water consumes chlorine faster, promotes algae growth, and shifts your LSI balance. We record temperature at every visit because it changes how we interpret every other reading on the report.
Free Chlorine(FC)
Free chlorine is the active sanitizer in your water - the chlorine that is available to kill bacteria, viruses, and algae. This is the most important reading on the report. If FC drops below the minimum, the pool is not sanitary.
Total Chlorine(TC)
Total chlorine is the sum of free chlorine and combined chlorine (chloramines). When TC is significantly higher than FC, it means chloramines have formed - the compounds responsible for the "chlorine smell" and eye irritation. The difference between TC and FC is your combined chlorine reading.
pH
pH measures how acidic or basic the water is on a scale from 0 to 14. Traditional charts show chlorine becoming ineffective above 7.6, but those numbers assume no CYA in the water. With CYA present (as in most pools), chlorine remains effective at higher pH because CYA slows its release rate. Salt pools naturally run higher pH (7.6-8.0) due to the electrolysis process, and this is normal when the LSI is balanced.
Cyanuric Acid(CYA)
CYA is chlorine's sunscreen. It shields free chlorine from UV degradation. Without it, sunlight destroys chlorine in hours. But too much CYA suppresses chlorine's killing power, a condition called chlorine lock. In spring through fall when UV and temperatures are high, target 30-50 ppm. In winter, CYA can run lower because UV intensity drops and cooler water consumes less chlorine.
Total Alkalinity(TA)
Alkalinity is the water's pH buffer. It resists rapid pH swings caused by rain, chemicals, or bather load. Low TA makes pH unstable and difficult to control. High TA pushes pH upward and can cause cloudy water and scale formation. TA also factors into the LSI calculation - when calcium is high, we lower TA to compensate to keep the index balanced.
Calcium Hardness(CH)
Calcium hardness is the most stable parameter in your water and forms the foundation for LSI balance. Unlike pH and alkalinity, it does not fluctuate day to day. Too little calcium makes the water aggressive - it will dissolve calcium from plaster, grout, and stone. The ideal CH target shifts with water temperature: colder water needs higher calcium (300–350 ppm) to prevent the LSI from dropping into the corrosive range.
Salinity(Salt)
For salt chlorine generator pools, salinity must stay within the manufacturer's specified range for the cell to produce chlorine efficiently. Too low and the cell can't generate enough chlorine. Too high and you risk corrosion and voiding the equipment warranty.
Total Dissolved Solids(TDS)
TDS represents everything dissolved in the water: minerals, salts, chemicals, and organic compounds. As TDS rises, water chemistry becomes harder to manage and chlorine efficiency decreases. Salt pools naturally have higher TDS because the salt itself counts.
Phosphates
Phosphates are a nutrient source for algae. They enter the pool from municipal water, fertilizer runoff, leaves, and some pool chemicals. Phosphates don't directly harm swimmers, but elevated levels make algae outbreaks more likely by providing a food source even when chlorine is present.
Copper
Copper enters pool water from mineral sanitizer systems, copper-based algaecides, corroded heat exchangers, or source water. Small amounts are harmless, but elevated copper can stain pool surfaces green or blue and discolor blonde hair.
Iron
Iron enters from well water, corroding equipment, or source water. Even trace amounts can cause rust-colored staining on pool surfaces, especially when chlorine oxidizes the iron.
Why Does Grey Shark Use the LSI Instead of Simple Ranges?
Most pool companies evaluate each chemical in isolation: "Is the pH in range? Is the calcium in range?" We take a different approach. Grey Shark Pool Services uses the Langelier Saturation Index (LSI) to evaluate water balance as a system.
The LSI is a calculation that factors pH, temperature, calcium hardness, alkalinity, and TDS together to produce a single number. That number tells us whether the water is:
Corrosive - dissolves plaster, grout, and metal
Balanced - chemically stable and surface-safe
Scaling - deposits calcium on surfaces and equipment
This matters because individual readings can be "in range" while the overall water balance is corrosive or scaling. Two pools with identical pH can have completely different LSI values depending on temperature and calcium. The LSI gives us the full picture and drives the adjustments we make at each visit.