How to keep pool water clean
No jargon: the three parameters that matter, the order to adjust them in, and the weekly routine that prevents 90% of problems.
The three parameters that matter
Free chlorine (1 – 3 ppm)
The disinfectant. Below 1 ppm the water isn't protected; above 3 ppm it irritates eyes and skin.
pH (7.2 – 7.6)
The key parameter. With high pH chlorine barely disinfects; with low pH the water corrodes equipment and swimmers.
Total alkalinity (80 – 120 ppm)
The pH buffer. If it's low, pH swings every day and you'll never stabilize the water.
Always adjust in this order: alkalinity → pH → chlorine. Fixing them in that order avoids chasing readings all season. You'll find every range and frequency in detail in the complete pool maintenance guide.
The routine that prevents 90% of problems
2-3 times a week
- Measure chlorine and pH
- Empty the skimmer baskets
- Skim the surface with a leaf net
Once a week
- Measure alkalinity
- Clean the pump prefilter
- Vacuum the pool
- Brush the walls
- Clean the waterline
Every 1-2 weeks
- Backwash the sand filter (or sooner if the gauge rises 0.3-0.5 bar)
Monthly / long term
- Measure calcium hardness and cyanuric acid
- Check water level and pump condition
- Replace filter sand every 4-5 years
Mistakes that make pools more expensive
Adding chlorine without checking pH. This is the most common mistake: with high pH, chlorine gets wasted and the water turns green anyway. Test first, dose after.
Filtering too little. Chemistry doesn't replace circulation: water that doesn't move is a breeding ground. In summer, filtration hours ≈ water temperature (°C) ÷ 2.
Forgetting cyanuric acid. Chlorine tablets build it up over time; above 80 ppm chlorine gets locked. If you've used tablets for years, test it: you may need to replace part of the water.
Wondering what all this costs if a professional does it? We cover that in how much pool maintenance costs.
Keep reading: How much pool maintenance costs · Excel vs pool software · How to price pool maintenance · Pool opening checklist · Get pool maintenance clients
Frequently asked questions
How do you keep pool water clean?+
Test chlorine and pH 2-3 times a week, keep free chlorine between 1 and 3 ppm and pH between 7.2 and 7.6, filter enough hours (in summer, roughly the water temperature divided by 2), and clean the skimmer, baskets and floor regularly. Consistency beats any miracle product.
In what order should you adjust water parameters?+
First total alkalinity (80-120 ppm), then pH (7.2-7.6), and finally chlorine (1-3 ppm). Alkalinity stabilizes the pH, and correct pH lets chlorine actually disinfect. Adjust in a different order and you'll chase readings all season.
Why does my pool turn green even though I add chlorine?+
Almost always high pH: above 7.8 chlorine loses most of its disinfecting power and algae take over. Other common causes are excess cyanuric acid (which locks chlorine) and insufficient filtration. Test pH before adding more product.
How many hours should the pool filter run?+
The practical rule in summer: filtration hours ≈ water temperature (°C) ÷ 2. At 28°C water, that's about 14 hours split into two cycles (better than one long one). In winter you can cut this a lot if the water is balanced and treated with winterizer.
How do you keep water clean with salt chlorination?+
A salt chlorinator generates chlorine automatically, but it doesn't manage pH or alkalinity: you still need to test them. Also check the electrolysis cell (it scales up with calcium) and the salt level recommended by the manufacturer, usually between 4 and 6 g/l.
Do you work in pool maintenance?
Log the parameters of every visit from your phone and catch drift before the water turns green.