Water chemistry is the foundation of pool ownership. Correctly balanced water keeps swimmers healthy, protects equipment from corrosion and scale, preserves liner and surface life, and makes the pool comfortable to swim in. Imbalanced water does the opposite — it’s the single most common cause of premature equipment failure, liner damage, and swimmer complaints. Understanding what your service company is testing, what the target ranges are, and why they matter is how you know whether the chemistry is actually being managed or just being treated as a checkbox.
“I tell every pool owner the same thing: pH is the master variable. Everything else flows from pH. Chlorine is dramatically less effective at high pH — at pH 7.8, you have less than half the sanitizing power you have at pH 7.2 with the same chlorine level. People add more chlorine when what they actually need to do is bring the pH down. Understanding that relationship changes how you think about the whole system.”
— Adam, pool service specialist at Clark Pools in Owen Sound, with 15 years of experience in residential pool installation, service, and renovation in the local area, as seen on Netflix’s Hotel Makeover
Table of Contents
The Core Chemistry Parameters
What parameters are tested at each service visit?
A professional service company tests at minimum these parameters at every visit:
pH (target: 7.2–7.6):
The most important parameter. PH affects chlorine effectiveness, swimmer comfort, and equipment/surface protection. At pH below 7.0, water becomes aggressive — corroding metal equipment, etching plaster, and irritating eyes and skin. At pH above 7.8, chlorine effectiveness drops dramatically and scale begins to form on surfaces and equipment.
Free chlorine (target: 1–3 ppm for most pools):
The active sanitizer that kills bacteria and algae. Total chlorine minus combined chlorine (chloramines) equals free chlorine. Ask specifically whether the test measures free chlorine or total chlorine.
Total alkalinity (target: 80–120 ppm):
Alkalinity buffers the pH — it resists pH swings. Low alkalinity causes pH to bounce unpredictably (pH bounce). High alkalinity makes pH difficult to adjust and promotes scale formation.
Calcium hardness (target: 200–400 ppm for most pools; 150–250 for vinyl liner pools):
Calcium hardness affects both water comfort and surface protection. Very low calcium (soft water) causes water to leach calcium from plaster surfaces, creating pitting. Very high calcium contributes to scale formation.
Cyanuric acid / stabilizer (target: 30–50 ppm for outdoor chlorine pools):
Stabilizer protects chlorine from UV degradation — outdoor chlorine pools lose chlorine rapidly to sunlight without it. However, too much stabilizer (above 80–90 ppm) reduces chlorine effectiveness significantly. Stabilizer accumulates over time and can only be reduced by diluting the pool water.
What a good answer looks like: All five parameters tested at each visit, results documented in writing, with an explanation of any adjustments made and why.
Do you also test for metals (copper and iron)?
Metal contamination in pool water causes staining — green or blue-green staining from copper, brown or rust staining from iron. Copper can come from corroded heat exchanger components (particularly in low-pH water) or from algaecide products. Iron typically comes from well water or corroded iron components.
If your pool has well water fill or older equipment, ask whether metals are included in the testing panel.
Questions About Saltwater Pools
How is a saltwater pool different to manage chemically?
A saltwater pool is still a chlorine pool — the salt chlorine generator (electrolytic cell) converts dissolved salt (sodium chloride) into chlorine. The chemistry parameters are the same as a conventional chlorine pool, but there are additional considerations:
Salt level (target: typically 2,700–3,400 ppm depending on the system):
If salt level is too low, the generator can’t produce adequate chlorine. If too high, it can damage equipment and make water taste noticeably salty.
Cell output setting: The generator’s output percentage needs to be adjusted seasonally — higher in summer when the pool is warm and being used heavily, lower in spring and fall.
Cell cleaning: The electrolytic cell accumulates calcium scale over time and needs to be cleaned (acid-washed) periodically — typically once or twice per season.
Ask how salt levels, cell output, and cell maintenance are managed as part of the service.
What is the expected life of the salt cell, and how much does replacement cost?
Salt chlorine generator cells typically last 5–7 years. Ask how old the current cell is and what replacement costs approximately.
Questions About Algae
What causes algae, and how is it treated?
Algae growth is almost always caused by inadequate sanitizer levels (low free chlorine), insufficient circulation, or phosphate buildup in the water. Ask the company:
- What is the protocol for treating a pool that has developed algae?
- Do you test for phosphates? (Phosphates are a nutrient source for algae; high phosphate levels can cause persistent algae problems even at adequate chlorine levels)
- What preventive algaecide program do you recommend?
How is a green pool (severe algae) recovered?
A pool that has turned green requires a more aggressive treatment — “shocking” (adding a large dose of chlorine or non-chlorine shock), running the filter continuously, and possibly multiple treatments over several days. Ask what the protocol is and what the approximate cost of a green pool recovery service is.
Questions About Chemicals
What chemicals do you use, and can you explain the rationale for each addition?
Ask the service company to explain each chemical they add during a service visit:
- What is it?
- What parameter is it addressing?
- What was the test result that prompted the addition?
A professional technician can explain each chemical addition in plain language. A technician who adds chemicals from habit rather than in response to test results is not managing your pool — they’re performing a routine.
Are the chemicals you’re using appropriate for my pool type?
Some chemicals are not appropriate for all pool types:
Trichlor tablets (high-stabilizer chlorine): Appropriate for pools with low or normal stabilizer levels. In pools that already have adequate stabilizer, continued trichlor use builds stabilizer to levels that reduce chlorine effectiveness — requiring partial water drain and refill.
Copper-based algaecides: Can stain surfaces and equipment at high concentrations. Use with caution in pools with high pH or low chlorine.
Calcium hypochlorite shock: Not appropriate for very high-calcium pools — adds calcium. Appropriate for low-hardness pools.
Ask whether the chemicals being used are matched to your pool’s specific conditions.
Related Questions
- Questions to Ask a Pool Service Company Before You Hire One
- How Do I Know If My Pool Water Is Safe to Swim In?
- Red Flags When Hiring a Pool Service Company
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