Let’s be honest — if your pool chemistry’s off, everything else gets harder. Filters struggle, clients complain, and your week gets longer.
But when water chemistry is dialed in? You get clear pools, happy customers, and fewer headaches. I’ve learned over the years that understanding (and being able to explain) pool chemistry is one of the best ways to set yourself apart as a true pro in this industry.
In this guide, I’ll break down what you really need to know: testing, balancing, troubleshooting, and adjusting for the seasons — so you can handle just about anything the water throws at you.
Water Testing Fundamentals for Pool Professionals
Essential Testing Equipment
To accurately diagnose water problems, you need the right gear. Here are the go-to options:
- Liquid test kits (drop-based): Highly accurate when used properly and ideal for daily field use, just keep the reagents fresh.
- Digital photometers: Excellent for techs who want fast, lab-grade precision and data logging, but they’re expensive.
- Test strips: OK for a quick read, but not ideal for full diagnosis or professional reports. These are reliably unreliable.
Proper Testing Procedures and Frequency
- Test at every visit, especially for chlorine, pH, and total alkalinity.
- Take water samples 18 inches below the surface (elbow deep) and away from returns.
- For commercial accounts, log results consistently to stay compliant and catch trends.
How to Explain Test Results to Customers
I like to think of this as part chemistry, part customer service. Don’t just say “pH is low” — say what that means for their pool. This builds major trust:
- “Your pH is low, which means the water’s a little acidic. That can wear down plaster and metal over time.”
- Educate your customer on why you’re adding a certain chemical, not just what you’re adding.
How to Balance Core Pool Water Parameters
Chlorine and Sanitizer Management
- Free chlorine: The active sanitizer. Ideal range: 1–3 ppm for residential, 3–5 ppm for commercial.
- Combined chlorine: Byproduct of used chlorine (causes odor). Keep under 0.2 ppm.
- Total chlorine = free + combined.
My Pro Tip: If combined chlorine is high, perform breakpoint chlorination (aka shocking) to restore balance.
See Related:
— How to Shock a Pool
pH Balance
- Ideal range: 7.4–7.6
- Low pH = corrosive water
- High pH = chlorine becomes a lazy employee — it’s there, but not working effectively.
Reminder: pH directly affects chlorine’s power — at 8.0, chlorine is only ~20% effective!
See Related:
— How to Raise pH in a Pool
— How to Lower pH in a Pool
Total Alkalinity (TA)
- Ideal range: 80–120 ppm
- TA stabilizes pH — too low and pH will bounce, too high and pH becomes resistant to change.
- Use baking soda to raise TA, muriatic acid to lower it. Slow and steady wins here.
See Related:
— How to Raise Alkalinity in a Pool
Calcium Hardness
- Ideal range: 200–400 ppm
- Low hardness = etching and corrosion
- High hardness = scaling on tiles, heaters, and plaster
My Pro Tip: If you’re working in areas with hard tap water (like I do), this one needs extra attention.
Stabilizer (Cyanuric Acid)
- Protects chlorine from UV burn-off.
- Ideal range: 30–50 ppm for most pools.
- Too much CYA can lock up chlorine — watch for this in pools using stabilized tabs.
Common Pool Water Problems and How to Fix Them
Cloudy Water
Start by checking your filter system, then look at pH and chlorine levels. Clarifiers can help, but you don’t want to treat the symptom — find the cause.
Causes
- Poor filtration
- High pH or high calcium
- Low sanitizer
- Debris and organics
Solutions
- Check and clean filters
- Adjust pH and chlorine levels
- Use clarifier or flocculant as needed
Algae Outbreaks
Types
- Green algae: common, fast-growing (easy fix)
- Mustard algae: yellow, clings to walls (more stubborn)
- Black algae: stubborn, root-like structure (bring your A-game)
Treatment
- Brush aggressively
- Shock with appropriate dosage
- Use algaecide that matches the issue and follow up with filter clean
My Pro Tip: Treat mustard and black algae with targeted algaecides and longer contact time.
Stains and Scale
Causes
- Metals in water (iron, copper)
- High calcium or pH
- Local water source or poor fill water
Fixes
- Use stain and scale remover
- Adjust water balance to prevent recurrence
- Consider adding sequestering agents during startup or after refills
Post-Rain or High Bather Load Issues
- Test water immediately after major storms or parties
- Expect diluted chlorine, pH shifts, and possible contamination
- Shock and rebalance as needed
Seasonal Adjustments for Pool Water Chemistry
Opening and Closing a Pool
- At opening, test everything — especially CYA and calcium.
- Add startup dose of algaecide, shock, and balance all levels.
- For closing, lower water level (if needed), add winterizing chemicals, and use metal sequestrant to prevent staining.
See Related:
— How to Open a Pool
— When to Close Your Pool
Summer vs. Winter Chemistry
- Hot weather = faster chlorine burn, more frequent testing.
- Cold water holds chlorine longer but can lead to scale if pH and calcium aren’t adjusted.
Adjust for Regional Conditions
- Dry/hot climates (e.g., Arizona): watch for evaporation, calcium buildup.
- Humid/rainy areas: be prepared for dilution and low chlorine.
- Freezing regions: ensure proper winterization and off-season maintenance checks.
The Wrap-Up: Systematize Your Chemistry Game
The best techs I know treat chemistry like a system. They test consistently, explain things clearly, and adjust slowly and smartly. A consistent, informed approach to pool chemistry saves time, prevents problems, and strengthens your relationship with clients.
When you can troubleshoot water issues confidently and explain the “why” behind your treatments, customers see you as the expert — not just the “pool guy” which allows you to retain more customers and charge higher premiums.
Read Next:
— Marketing Strategies for New Pool Service Businesses
— Scaling Your Pool Business: From Solo Operator to Managing a Team
— How to Diagnose Complex Pool Equipment Issues
Main Image: Pool-related equipment laid by the pool for service and maintenance. Photo Credit: oneSHUTTER oneMEMORY / Adobe Stock Free / License
Related Posts:
