pH
pH affects swimmer comfort and sanitizer effectiveness. If it is outside the required range, correct it before further treatment.
Pool care
Water care
Pool water chemistry: what to test and how to adjust it
Test the water before adding anything. Adjust pH, check the sanitizer level and make sure filtration is working properly. Use chemicals to correct a measured problem, not just a change in how the water looks.
The basics
Four checks before adding chemicals
Understanding your readings makes it easier to choose the right treatment. A change in water colour is a reason to investigate, not enough information to choose a dose.
Free chlorine
Free chlorine is the chlorine available to disinfect the water. Test it before dosing so you know whether an adjustment is needed.
Alkalinity
Alkalinity helps keep pH stable. If pH keeps changing, check alkalinity before repeatedly adding pH adjuster.
Filtration
Chemicals cannot make up for poor flow, a dirty filter or too little pump runtime. Water needs to pass through the filter for particles to be removed.
What to do next
A practical water-care routine
Make each adjustment in the right order and allow the required time before retesting. Adding more products too soon can waste chemicals without solving the problem.
Test the water
Use suitable test strips, drop reagents or a digital tester. Testing tells you which treatment, if any, is needed.
Adjust pH first
Correct pH before carrying out a major chlorine, algae or cloudy-water treatment, following the product instructions.
Check the sanitizer level
Once you know the pH and free chlorine level, you can decide whether the pool needs an adjustment, a shock treatment or routine maintenance.
Keep filtration working properly
Circulate the water after treatment as instructed. Clean or backwash the filter when needed.
Pool chemicals
What common pool chemicals are used for
Product names vary, but their main uses are balancing the water, disinfection, algae control and removing fine particles.
pH reducer / pH increaser
These products lower or raise pH. Follow the label, make controlled adjustments and test again between doses.
Chlorine
The primary sanitizer in many home pools. The formulation and strength vary by product.
Algaecide
A supplemental treatment to help control algae. It does not replace testing, chlorine or filtration.
Flocculant
Clumps fine particles together so they can be removed by filtration or vacuuming, where the product is compatible with the system.
Common mistakes
Common chemical-handling mistakes
Handle pool chemicals carefully and follow the product label. Never combine products unless the manufacturer's instructions explicitly allow it.
- 1adding chemicals without testing first
- 2shock treating while pH is outside the required range
- 3running the filter for too little time after treatment
- 4mixing different products in a bucket or skimmer
- 5guessing doses without knowing the pool volume
- 6ignoring a dirty filter or poor flow
Next steps
Help with specific water problems
How much chlorine to add
See the formula, worked examples and safe dosing instructions.
Learn morePool chemical dosing calculator
Estimate a chlorine adjustment using the pool volume and the product's stated strength.
Learn moreGreen water
If the water has turned green, check for algae and test pH and chlorine. Inspect the filtration too.
Learn moreCloudy water
If the water is cloudy rather than green, check pH, filtration and suspended particles.
Learn moreHow to shock a pool
When shock treatment is appropriate, how to apply it and what to check before swimming again.
Learn moreFilling a pool for the first time
Start the system and balance newly added water without mixing treatments or adding them all at once.
Learn moreChlorine tablets or granules
Compare active ingredients, stabilizer content, dosing methods and storage requirements.
Learn moreHow to lower pH
Check alkalinity, adjust in stages and test again before adding more.
Learn moreWhen to swim after adding chlorine
Wait for the label's stated time, then check free chlorine, pH and water clarity.
Learn morePractical answers
Pool chemistry: common questions
What should you test first in a pool?
Start with pH and free chlorine. Check alkalinity as well, especially if pH is difficult to keep stable.
Will algaecide clear green pool water?
It may help, but algaecide alone is not a complete treatment. Check pH, sanitizer, filtration and the amount of organic debris in the pool.
Why should you test before adding pool chemicals?
The same symptom can have several causes. Without a test, it is easy to choose the wrong product or add too much.
Can filtration replace pool chemicals?
No. Filtration removes particles, but you still need to disinfect the water and maintain its chemical balance.