Your field test kit measures the basics: free chlorine, total chlorine, pH, total alkalinity, calcium hardness, and CYA. That covers most of what matters for routine maintenance. But for persistent water quality problems, troubleshooting staining, verifying that a chemical correction worked, or providing professional-grade documentation for a commercial account, a comprehensive laboratory analysis provides data your kit simply cannot. Here is what the report contains and how to use it.
A full pool water laboratory analysis typically includes the following parameters:
The Langelier Saturation Index is a calculated value (not directly measured) that predicts whether the water will tend to deposit calcium carbonate scale (positive LSI) or dissolve calcium carbonate from surfaces (negative LSI). The ideal target is -0.3 to +0.3.
The LSI on a lab report is calculated from the measured values at laboratory temperature and conditions. If your pool temperature is significantly different from the lab conditions, the reported LSI may not fully reflect actual pool behavior. Many labs now correct for your specified pool temperature — provide this when submitting the sample.
Total dissolved solids is the cumulative concentration of everything dissolved in the water — minerals, chemical additions, bather waste, oxidation byproducts, fill water impurities, and the salts from every chemical that has ever been added. TDS rises over the pool's life and is only reduced by dilution (partial drain and fresh water addition).
| TDS Level | Condition | Action |
|---|---|---|
| Below 2,000 ppm above fill water TDS | Normal | No action required |
| 1,500–2,500 ppm above fill water TDS | Marginal | Consider partial drain at next opportunity |
| Above 2,500 ppm above fill water TDS | High | Partial drain required; chemistry becoming unresponsive |
Note: salt pools have naturally elevated TDS (3,000–5,000 ppm from the salt alone) — the high-TDS threshold above refers to non-salt pools. Salt pool TDS must be evaluated separately, excluding the salt contribution.
The metals panel (iron, copper, manganese) is the most actionable part of a lab report for staining problems. Results are reported in parts per million (ppm) or micrograms per liter (µg/L):
Phosphate is an algae nutrient. While chlorine can control algae regardless of phosphate level (if maintained correctly), high phosphate levels above 500 ppb increase the chlorine demand needed to maintain control and may contribute to chronic algae issues in pools with inadequate circulation. Phosphate removal products (lanthanum-based) remove phosphates effectively and are worth recommending when lab results show levels above 1,000 ppb in problem pools.
Store lab reports, track TDS trends over seasons, and correlate lab results with field test data. SplashLens keeps your service documentation organized and accessible offline. Free for pool service professionals.
Open SplashLens Free →Send water to a lab at least once per season for residential pools, at pool opening or closing, after any significant water quality problem (algae outbreak, persistent cloudiness, unexplained staining), and after major water replacement. Commercial pools should perform more frequent lab verification (monthly or quarterly depending on volume and bather load).
TDS (total dissolved solids) is the total concentration of all dissolved substances in the water. As TDS rises above 2,000 ppm above fill water TDS, the water becomes less responsive to chemical treatment, cloudy, and harder to balance. High TDS is only fixed by partial drainage and dilution.
Yes. A comprehensive lab panel includes testing for iron, copper, manganese, and other metals that cause staining. Field test kits can detect iron and copper, but lab quantification is more accurate for determining whether chelation/sequestration treatment is needed and how much.
Use the lab's provided sample bottle or a clean plastic bottle. Collect the sample from elbow depth (about 18 inches below the surface) at a point away from returns and skimmers. Do not collect from the surface — it gives unrepresentative chemistry. Label the sample immediately and deliver to the lab within 24 hours of collection.