Every pool problem you can see — cloudy water, green tint, itchy skin, scale on tiles, a smell of "too much chlorine" — traces back to one of five numbers. Learn these and you can hold a conversation with any vendor on equal footing.
1. Free chlorine: 1 to 3 ppm
This is your active sanitiser. Below 1 ppm, bacteria and algae start winning. Above 5 ppm, water becomes harsh on skin, eyes and swimwear. Note the word free — a test that reports only total chlorine hides the problem.
2. Combined chlorine (chloramines): below 0.5 ppm
That sharp "chlorine smell" is not chlorine. It is chloramine — chlorine already bound to sweat, urine and organics, and largely spent. High combined chlorine means the pool needs shocking, not more routine dosing.
3. pH: 7.2 to 7.6
pH decides whether your chlorine works at all. At pH 8.0, the same chlorine is a fraction as effective. Low pH is worse in a different way: it etches plaster, corrodes metal fittings and degrades pump seals. This is the number to correct first, every time.
4. Total alkalinity: 80 to 120 ppm
Alkalinity is pH's shock absorber. Too low and pH swings wildly after every rainfall or dose — "pH bounce". Too high and pH becomes stubborn, drifting upward and causing cloudiness. Fix alkalinity before chasing pH.
5. Calcium hardness: 200 to 400 ppm
Critical across Delhi NCR, where source water is hard. Too high and you get scale on tiles, inside heaters and across filter media. Too low and the water pulls calcium out of the plaster itself.
Bonus: TDS and cyanuric acid
Total dissolved solids above roughly 1,500 ppm above the fill-water baseline makes chemicals sluggish and water dull; the cure is partial dilution. Cyanuric acid (30 to 50 ppm) shields chlorine from sunlight, but overdosed it locks chlorine up entirely — "chlorine lock".
The order of operations
Test, then correct alkalinity, then pH, then sanitiser, then hardness and stabiliser. Correcting out of order means undoing your own work.
Every SwimCompany visit logs all of these readings against ideal ranges in your dashboard, so you can see trends instead of guessing.