Here's the whole chart first, then the explanations. These are the ranges this site's calculators aim for — the same figures the water test dashboard uses when it tells you what to add, generated from the same source so they can't disagree.
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| Reading | Range | Aim for | Why it matters |
|---|---|---|---|
| Free chlorine (FC) | Depends on CYA — see below | The only thing sanitizing the water | |
| pH | 7.2–7.8 | 7.5 | Comfort, and whether the water eats or coats surfaces |
| Total alkalinity (TA) | 60–90 ppm 60–80 with a salt system | 70 ppm | Keeps pH from wandering |
| Cyanuric acid (CYA) | 30–50 ppm 60–80 with a salt system | 40 ppm | Shields chlorine from sunlight — and sets your FC target |
| Calcium hardness (CH) | 250–450 ppm lower is fine on vinyl | 350 ppm | Scale versus etching on plaster and equipment |
| Salt | 2,700–3,600 ppm | 3,200 ppm | Feedstock for a salt chlorine generator — check your cell's manual |
| Combined chlorine (CC) | Under 0.5 ppm | 0 | Anything higher means chlorine is losing a fight |
| Water balance (CSI) | −0.3 to +0.3 | 0 | The verdict all the others add up to |
Chlorine: the number with no fixed answer
Notice the chart refuses to give a single figure for chlorine. That's the most important thing on this page, and it's where most charts elsewhere are simply wrong. The right FC depends on your CYA, because stabilizer binds chlorine into a protected reserve — useful against sunlight, but it means a pool at CYA 80 needs far more total chlorine than one at CYA 30 to have the same sanitizing strength.
| If CYA is | Minimum FC | Target FC | With a salt system | Shock level |
|---|---|---|---|---|
| 20 ppm | 2 | 4 | 3 | 10 |
| 30 ppm | 2.5 | 4 | 3 | 12 |
| 40 ppm | 3 | 4.5 | 3 | 16 |
| 50 ppm | 4 | 6 | 3.5 | 20 |
| 60 ppm | 4.5 | 7 | 4 | 24 |
| 70 ppm | 5.5 | 8 | 5 | 28 |
| 80 ppm | 6 | 9 | 5.5 | 32 |
| 90 ppm | 7 | 10.5 | 6.5 | 36 |
All figures ppm. Minimum is the line below which algae gets a foothold — it's a floor to stay above, not a goal to sit on. Chlorine target depends on CYA: there is no single correct FC number.
That familiar advice predates widespread stabilizer use, and it's still printed on packaging and repeated at pool stores. It's fine for an indoor pool with no CYA. In a stabilized outdoor pool it describes a level that is often below the algae threshold — which is why so many people hold "perfect" chlorine all week and still go green in July. If you take one number away from this page, make it your CYA, because you can't interpret your chlorine reading without it.
Working backwards: what you're seeing, and what to test
A chart tells you what the numbers should be. Most people arrive with the opposite problem — something looks wrong and they don't know which reading explains it. This is that lookup in reverse:
| What you're seeing | Usually means | Test these first |
|---|---|---|
| Green water, or green tint on the walls | FC has been below minimum for your CYA | FC, then CYA |
| Cloudy water, filter running fine | Scaling water, or chlorine losing a fight | CSI (pH, TA, CH), then FC and CC |
| Strong "chlorine" smell | Combined chlorine — too little free chlorine, not too much | CC, then FC |
| Stinging eyes, itchy skin | pH out of range, usually low; sometimes high CC | pH, then CC |
| Chlorine disappears within a day | CYA too low to protect it, or something is consuming it | CYA, then the overnight test |
| FC won't rise no matter what you add | Ammonia or a heavy algae load eating it on contact | CC, CYA — expect a SLAM |
| White crust at the waterline or in the cell | Scaling — calcium coming out of solution | CSI, CH, pH |
| Rough, etched plaster; corroded metal | Aggressive water dissolving your surfaces | CSI, CH, TA |
| pH climbs back up every few days | High TA, new plaster, a salt cell, or water features aerating | TA, then pH |
| Salt system reports low salt, strips say fine | A scaled or aging cell, not a salt shortage | Salt by test kit, then CSI |
| Walls feel slippery | Early algae, before it's visible | FC against your CYA |
Two patterns worth noticing: almost every problem starts with FC or with the saturation index, and a "chlorine smell" always means you need more chlorine, never less.
How to take a sample that tells the truth
Every number on this page assumes the water in your test vial represents the pool. Often it doesn't, and a bad sample looks exactly like bad chemistry — you end up dosing to fix a reading rather than a problem.
Where to collect it. Elbow-deep — about 18 inches down — and well away from returns, the skimmer, and any floating dispenser. Surface water has been sitting in the sun, water beside a return is whatever you added most recently, and water near a puck floater is a little pocket of concentrated chemistry that exists nowhere else in the pool. Rinse the vial with pool water before filling it.
When. After the pump has run long enough to mix the pool — an hour is plenty — and before you add anything that day. If you've just dosed, wait for circulation; testing 20 minutes after pouring acid tells you about the acid, not the pool.
What can betray you. Reagents expire, and DPD in particular fades with age and heat — a bottle that spent last summer in a hot shed will read low and make you overdose. Replace reagents yearly. Test in shade rather than glaring sun, read colors promptly, and if a result surprises you, run it twice before acting on it.
Test strips are fine for a quick pH and a rough chlorine check. What they can't do is measure high FC — most top out around 10 ppm, and color matching gets vague well before that. Since shock levels start at 12 ppm and climb with your CYA, a strip physically cannot tell you whether a SLAM is working. That's the one job that needs a FAS-DPD drop kit, and it's the reason the guide on shocking a pool treats the test kit as part of the method rather than an accessory.
Not every reading deserves the same attention
A chart makes eight numbers look equally urgent. They aren't. In practice they sort into three tiers:
| Tier | Readings | What happens if you ignore them |
|---|---|---|
| Check constantly | FC, pH | Days matter. Low FC means algae within a week; wrong pH is uncomfortable and quietly damaging |
| Check regularly | TA, CYA | Weeks matter. These set how stable everything else is |
| Check occasionally | CH, salt, CSI | Months matter. Slow-moving, and mostly about protecting surfaces and equipment |
How often to actually test
| Reading | In season | Off season |
|---|---|---|
| Free chlorine | 2–3× a week (daily if it's dropping) | Every week or two |
| pH | 2–3× a week | Every week or two |
| Total alkalinity | Every week or two | Monthly |
| CYA | Monthly, and after adding stabilizer | At opening |
| Calcium hardness | Monthly | At opening and closing |
| Salt | Monthly | At opening |
Also test after heavy rain, a big pool party, topping up a lot of water, or anything unusual — those are the events that move numbers fast.
The order to fix things in
When several readings are off at once, sequence saves you work, because some adjustments move others:
- Chlorine first if it's at or near zero. An unsanitized pool is the only genuine emergency here.
- CYA next if it's very low or very high, since it decides what your chlorine target even is.
- Then pH — most other chemistry behaves better in range, and test kits read more reliably.
- Then alkalinity, which will have moved while you adjusted pH.
- Calcium and salt last. They drift slowly and rarely need urgent action.
One chemical at a time, with the pump running, and retest before repeating a dose. The dashboard works through them in this order automatically if you enter everything at once.
A reading slightly outside a range is a nudge, not an alarm. TA at 95 with a stable pH is fine; chasing it to 70 with a weekend of acid dosing is effort spent for nothing. The exception is chlorine, where the minimum genuinely is a line — below it, algae has an opening, and the cost of being wrong is a week of recovery rather than a slightly imperfect number.
Readings you can mostly ignore
Pool stores test for more than this chart lists, and most of the extras exist to sell a product rather than to solve a problem you have:
Phosphates. Yes, algae eats phosphates. No, removing them isn't how you control algae — chlorine is. A pool held at proper FC will not grow algae at any realistic phosphate level, and phosphate remover is an expensive way to treat a symptom of a chlorine problem. Fix the chlorine, and the phosphate reading stops mattering.
TDS (total dissolved solids). In residential pools this is a number in search of a meaning. It rises harmlessly over time, and in a salt pool it's high by definition because you deliberately added salt. A high TDS reading alone is not a reason to drain.
Copper and mineral systems. These reduce how much chlorine you need rather than replacing it, and copper brings its own risk of staining plaster and turning blonde hair green. They're an addition to chlorine chemistry, not an escape from it.
Borates are a genuine exception: optional, real, and useful — they buffer pH from the top and make a salt pool much less demanding. Just not necessary, and worth having after the basics are steady rather than before.
Where these numbers come from
The ranges here follow standard industry practice and the FC/CYA relationship developed and documented by the Trouble Free Pool community, which is what changed how stabilized pools are managed. Alkalinity, calcium and saturation-index guidance follows the same chemistry behind Taylor's watergram. Where a manufacturer specifies something different for your equipment — a salt cell with its own salt window, most obviously — the manufacturer wins.
Every figure on this page is generated from the same target definitions the calculators use, so the chart and the tools cannot drift apart. If you think one of these ranges is wrong, we'd genuinely like to hear it — the about page explains how corrections work.