How the chemistry recommendations are computed

Every time you record a chemistry test on the Pool dossier, the platform computes what to add (or stop adding) to bring your pool back into range. The math behind it isn't magic — it's the same volume + chemistry calculations a pool store does on their counter, just automated.

The five core test parameters and their target ranges:

| Parameter | Ideal | Lower bound | Upper bound |
|---|---|---|---|
| Free Chlorine | 2.0 – 3.0 ppm | 1.0 | 4.0 |
| pH | 7.4 – 7.6 | 7.2 | 7.8 |
| Total Alkalinity | 80 – 120 ppm | 60 | 180 |
| Calcium Hardness | 200 – 400 ppm | 150 | 500 |
| Cyanuric Acid (CYA) | 30 – 50 ppm | 20 | 80 |

(Salt-water generator pools have one more: Salt, target 2700-3400 ppm depending on cell.)

How recommendations are derived:

1. **Read your pool volume** — set once on the pool basics card. Recommendations scale to pool size.
2. **Apply the test** — you enter measured values from your test strip / drop kit / Taylor K-2006.
3. **Compute deltas** — for each parameter, what's the gap to ideal?
4. **Compute corrections** — given your pool volume + chemical dosing math:
- To raise chlorine: amount of liquid chlorine (12.5% sodium hypochlorite) or shock (dichlor / cal-hypo) to add.
- To raise pH: soda ash (sodium carbonate); to lower: muriatic acid or dry acid.
- To raise alkalinity: sodium bicarbonate; to lower: muriatic acid (slow-add, aerate).
- To raise calcium hardness: calcium chloride.
- To raise CYA: stabilizer (cyanuric acid powder).
5. **Show the action card** — "Add 14 oz of muriatic acid to bring pH from 7.9 to 7.5." With a "Do It" button that creates a service-log entry once you've actually added it.

The Langelier Saturation Index (LSI):

The big picture metric the platform tracks: LSI tells you whether your water is corrosive (negative LSI), balanced (zero), or scaling (positive). Computed from pH, alkalinity, calcium hardness, CYA, water temperature, and salinity. LSI between -0.3 and +0.3 is the safe range; outside that you risk plaster damage (negative) or scale buildup (positive).

When the platform won't auto-recommend:

- **Stabilizer (CYA) lock-in** — CYA is forever in your pool until you drain. The platform won't recommend adding CYA if you're already over 50 ppm; it'll recommend partial drains instead.
- **Conflicting corrections** — if your pH is high AND your alkalinity is low, you can't just dump acid (drops both). The platform recommends a two-step approach: add baking soda first, then re-test, then adjust pH.
- **CYA below 30** with chlorine corrections — the platform warns that chlorine without stabilizer burns off in sunlight; recommends CYA first.

If you use a salt-water generator (SWG):

The recommendations engine knows about your generator's output rating and adjusts. Less liquid chlorine recommended (the cell makes it), more attention to salt (the cell needs ~3000 ppm), and SWG-specific tasks (cell inspection / cleaning at 6-month interval).

What you can ignore:

The recommendations are starting points, not absolutes. If you've been running a pool for years and know the quirks of your specific system, override. Recommendations remember a user's overrides — over time, the engine learns your patterns.