Ideal Pool Chemistry Levels (Chart)
Clear, comfortable pool water comes down to six numbers. Keep them inside their ranges and the pool mostly looks after itself; let one drift and the others usually follow. This guide puts every target in one chart, explains what each number actually does, and points you to the calculator that fixes it.
Pool chemistry chart
| Parameter | Acceptable range | Ideal |
|---|---|---|
| Free chlorine (FC) | 1–4 ppm | 2–4 ppm, or about 7.5% of CYA |
| pH | 7.2–7.8 | 7.4–7.6 |
| Total alkalinity (TA) | 60–120 ppm | 80–100 ppm (60–80 for salt pools) |
| Calcium hardness (CH) | 150–400 ppm | 250–350 ppm plaster; 150–250 ppm vinyl/fiberglass |
| Cyanuric acid (CYA) | 30–80 ppm | 30–50 ppm (chlorine); 60–80 ppm (salt) |
| Salt (SWG pools) | 2,700–3,400 ppm | 3,000–3,200 ppm (check your cell's manual) |
Residential pool targets as commonly published by the Pool & Hot Tub Alliance (ANSI/APSP/ICC-5 residential guidance) and Trouble Free Pool. pH range also matches the CDC Model Aquatic Health Code (7.2–7.8).
These are targets for residential outdoor pools. Public pools follow local health codes, and indoor pools need little or no stabilizer. Your salt cell’s manual overrides the salt range, and your plaster or liner manufacturer may give its own calcium range.
Free chlorine (FC)
Free chlorine is the sanitizer that is still available to kill bacteria and algae. The right level is not a fixed number: it depends on how much stabilizer (CYA) is in the water, because CYA holds part of the chlorine in reserve and slows it down.
A practical rule, popularized by the Trouble Free Pool community, is to keep free chlorine at no less than 7.5% of your CYA level. At CYA 40 ppm that is 3 ppm; at CYA 80 ppm it is 6 ppm. Shocking takes roughly 40% of CYA.
To work out a dose for your pool, use the pool chlorine calculator. It accounts for product strength, so 12.5% liquid chlorine, household bleach and cal-hypo all give the right amount.
pH
pH controls how well chlorine works and how the water feels. Below about 7.2 water becomes corrosive and stings eyes; above about 7.8 chlorine slows down, scale forms more easily and the water can turn cloudy. Most owners aim for 7.4 to 7.6.
pH is the number that moves most often, and the amount of acid or soda ash needed depends heavily on total alkalinity. The pool pH calculator models that buffer, so it gives a realistic dose instead of a per-gallon rule of thumb.
Total alkalinity (TA)
Total alkalinity is the pool’s pH buffer. Too low, and pH swings with every rainstorm or chlorine dose. Too high, and pH keeps creeping upward as carbon dioxide leaves the water, which wastes acid.
Pools with salt chlorine generators, fresh plaster or lots of water features usually do best at the low end (60–80 ppm), because those conditions push pH up. Raise TA with baking soda and lower it with acid plus aeration; the alkalinity calculator works out both.
Calcium hardness (CH)
Water that is low in calcium tries to dissolve it from somewhere, and in a plaster or pebble pool that somewhere is the pool surface. That is why plaster pools need more calcium than vinyl or fiberglass ones. Too much calcium, on the other hand, leads to scale on tile and inside heaters.
Calcium hardness only goes up (with calcium chloride, hard fill water and evaporation). The only practical way down is replacing part of the water.
Cyanuric acid (CYA, stabilizer)
Stabilizer protects chlorine from sunlight. Without it, an outdoor pool can lose most of its chlorine within hours on a sunny day. With too much, you need very high chlorine levels to stay sanitary and shocking becomes expensive.
Trichlor tablets and dichlor powder add CYA every time you use them, so levels creep up over a season. Salt pools usually run higher (60–80 ppm) because the cell produces chlorine continuously and benefits from more protection.
Salt
Only relevant if you have a salt chlorine generator. The cell turns dissolved salt into chlorine, and it needs salt within its working range to do that efficiently. Most cells want around 3,000–3,200 ppm, but check yours.
Putting it together: the saturation index
Calcium, pH, alkalinity and temperature interact. The Langelier Saturation Index (LSI) combines them into one number that tells you whether the water will etch surfaces (negative) or deposit scale (positive). Anything between −0.3 and +0.3 is considered balanced. Check yours with the LSI calculator, especially if you have a plaster pool or a heater.
In what order should you adjust?
- Total alkalinity first, because it sets how pH behaves.
- pH next, once TA has circulated for a few hours.
- Calcium hardness, pre-dissolved and added slowly.
- Stabilizer, which dissolves slowly; wait several days before retesting it.
- Free chlorine last, at the level your CYA calls for.
Add one product at a time with the pump running, wait between products, and retest before adding more. Never mix chemicals, and always add chemicals to water rather than water to chemicals.
How often to test
During the swim season, test free chlorine and pH frequently: daily or every other day is common for pools dosed by hand, a little less for salt pools with a stable routine. Test alkalinity, calcium and CYA every week or two, and salt monthly. Drop-based test kits are far more precise than strips, which matters when you are dosing by the ounce.
Quick troubleshooting
| What you see | Check first |
|---|---|
| Cloudy or green water | Free chlorine vs. CYA, combined chlorine, filter |
| Strong “chlorine” smell, red eyes | Combined chlorine (shock), pH |
| White scale on tile | pH, alkalinity, calcium (LSI) |
| Rough or etched plaster | Low calcium or low pH (LSI) |
| Chlorine gone by evening | Low CYA |
| pH rises every few days | High alkalinity, salt cell, aeration |