Cloudy Pool Water - Diagnostic Tree

Symptom

Pool water appears hazy, milky, or cloudy. Customer can no longer see the bottom of the deep end clearly. Visibility through pool water should be ≥ 8 ft in residential pools - anything less is a service call.

Likely Causes

In order of frequency for typical residential pools in summer:

• Imbalanced water chemistry - high pH, high calcium hardness, or improper sanitizer level (most common, ~70 % of cases)
• Filter failure - clogged cartridge / DE grid, malfunctioning sand filter, or undersized system
• Algae bloom in early stage - not yet green, but particulate already in suspension
• Recent heavy use - body oils, sunscreen, sweat from a pool party
• Fresh fill-water introduction - well water with high metals or municipal water with high calcium

Diagnostic Steps

1. Test chemistry first. Use a reliable test kit (Taylor K-2006 or equivalent - not the cheap test strips). Record:

• Free chlorine (target 1 - 3 ppm)
• pH (target 7.4 - 7.6)
• Total alkalinity (target 80 - 120 ppm)
• Calcium hardness (target 200 - 400 ppm)
• Cyanuric acid (target 30 - 50 ppm for outdoor pools)

1. Visually inspect the filter. Pressure reading should be within 5 psi of "clean filter" baseline. Higher = clogged. Lower = bypass or torn element.
2. Check the pump. Verify full prime, no air leak at the lid, normal flow on the return jets.
3. Look for waterline edge growth. A faint mustard-yellow or pink film at the waterline = algae starting; pool needs shock treatment regardless of chemistry numbers.
4. Ask the customer about recent activity. Pool party 24 - 48 hours prior is often the explanation; bather load alone produces visible cloud.
5. Inspect fill water. Run a test on tap water if recent top-off; high municipal calcium will cloud a pool within hours.

Resolution

Pick based on the diagnostic finding:

• High pH (> 7.8): dose with muriatic acid or dry acid per pool volume calculation. Run pump 24 hours.
• Low sanitizer + cloudy: shock with calcium hypochlorite or dichlor to 10 ppm; run pump 24 hours; brush walls.
• Clogged filter: backwash (sand / DE) or chemically clean cartridge per manufacturer instructions.
• Algae bloom: shock + algaecide; brush walls hard; vacuum to waste after settle.
• High calcium hardness (> 400 ppm): partial drain + dilute with low-hardness water. There is no "calcium reducer" chemical that actually works long-term.
• Bather load: oxidize with non-chlorine shock; advise customer on shower-before-swim etiquette.

Prevention

• Weekly chemistry test on every recurring service
• Filter pressure check + clean per the 5-psi rule
• Educate the customer on bather load + showering before swimming
• Annual partial drain (25 - 33 %) for pools in hard-water regions to manage calcium

References

• NSPF / PHTA Certified Pool Operator (CPO) manual
• Taylor Technologies test kit instructions for the K-2006