| Level | Yours | Ideal | Add this |
|---|---|---|---|
| Fill in the fields above. | |||
How the calculation works
Each reading is checked against the range it should sit in, and given one of three states: in range, low, or high. Nothing here is a single score out of ten — a pool with perfect chlorine and wrecked alkalinity is not "80% fine", it is a pool with an alkalinity problem.
The order things should be fixed in is fixed, and it is not the order the readings appear in: alkalinity, then pH, then calcium hardness, then cyanuric acid, then chlorine. Alkalinity is what holds pH steady, so correcting it first often moves pH into range without any separate adjustment. "Do this first" names whichever of those is furthest up that list and out of range.
Worked example
A pool reads 1 ppm chlorine, pH 7.9, alkalinity 70. Three readings, two obviously wrong, and the instinct is to add chlorine. But alkalinity sits above pH in the order, so it comes first — and raising it with baking soda will lift pH as a side effect. Fix alkalinity, run the pump, re-test, and the pH problem may already be gone.
Assumptions
- Readings were taken from water at least 12 inches below the surface, away from return jets and skimmers.
- Ranges shown are the commonly published targets for residential pools.
- Salt is only assessed when a reading is entered, since most pools are not saltwater.
Limitations
- A status of "in range" describes those readings at that moment. It is not a statement that the water is safe or sanitary.
- Cloudy water, algae and a strong chlorine smell are all problems this cannot see, because none of them show up in the numbers entered here.
- Test strips drift with age and heat. A drop-based kit is markedly more reliable for anything you intend to act on.
Questions people ask
Which reading should I fix first?
Alkalinity, then pH, then calcium hardness, then cyanuric acid, and chlorine last. The tool names the first one out of range for you.
Is my pool safe to swim in?
This tool can tell you whether the numbers you entered are in their usual ranges, which is not the same question. Free chlorine above 10 ppm or a pool that is visibly cloudy are both reasons to stay out regardless of what any calculator says.
Do I need to enter everything?
No. Leave any box empty and it is left out of the assessment. Chlorine and pH alone give a useful weekly check.
Why does water temperature matter?
Warm water burns through chlorine faster and helps algae get going. Above about 85°F, expect to hold chlorine at the upper end of its range and test more often.