No Chlorine Reading on a Salt Pool - Decision Tree

Why this matters

"My salt pool reads zero chlorine" is the most common emergency call between Memorial Day and Labor Day. The temptation is to dump a bucket of cal-hypo and walk; the actual problem is one of seven things and only one of them is "the SWCG is dead." Skipping the decision tree wastes a service call, hides the real fault, and on a CYA-loaded pool can swing free chlorine to 15+ ppm overnight. Work the tree in order - the first true answer is the cause about 80% of the time.

Step 1 - confirm the test, not the pool

DPD reagent older than 12 months reads low or zero on any chlorine level. Replace the reagent and retest before doing anything else. Cross-check with a fresh test strip; if the strip reads 1-3 ppm but the DPD reads 0, the DPD reagent is bleached out. Taylor K-2006 refills (R-0870 powder, R-0003 buffer, R-0871 thiosulfate) have a code-date on the bottle - reagents over 18 months from manufacture are suspect even unopened.

Confirm sample is from elbow-depth, mid-pool, not from the surface or the skimmer throat. Confirm the DPD-FAS titration is not stalling because total chlorine has slammed past combined - if the sample turns pink and then immediately back to clear before titration, you have a high CC reading masquerading as zero FC.

Step 2 - test stabilizer (CYA) and pH

CYA above 100 ppm "locks" chlorine - the SWCG can be running fine and a properly designed test will read very low free chlorine because the hypochlorous-acid fraction collapses. Use the Taylor 2005 turbidity test. If CYA is over 80, the only fix is a partial drain and refill. SWCGs are usually run at 70-80 ppm CYA; salt-pool owners often top off with stabilized chlorine pucks "as backup" and stack CYA past 150 without noticing.

pH above 8.0 also drops the active-chlorine fraction. If pH is high and CYA is normal, lower pH with muriatic acid first and retest in 24 hours before assuming the SWCG is bad.

Step 3 - inspect the salt cell visually

Shut the pump off. Unscrew the cell unions. Hold the cell up to the sun and look through the plates. You are looking for:

• White calcium scale on the plates - cell needs acid wash
• Plates worn thin (compare to a known-good cell of the same model) - cell at end of life
• Black flake (manganese / organic) on the plates - source water issue or low ORP for extended period
• Visible cracks or missing plates - replace cell

For a Hayward T-Cell-15 (P/N GLX-CELL-15-W), expected life is 10,000 hours / 3-5 seasons. For a Jandy AquaPure Ei (P/N R0452200), 10,000-12,000 hours. For a Pentair IntelliChlor IC40 (P/N 520555), 10,000 hours with the diagnostic LED telling you remaining life on press-and-hold.

Acid wash: 4 parts water to 1 part muriatic in a clean bucket, soak cell 10-15 minutes maximum, rinse thoroughly with fresh water. Never reverse the ratio - acid-first splashes etch the plates. Never wash a cell that is not scaled - you remove ruthenium coating.

Step 4 - check salt level and cell flow

Test salt with a calibrated digital tester (Hayward Aqua Trol GLX-CHEM4-W or AquaChek TruTest). Cells need:

• Hayward T-Cell-15: 2700-3400 ppm, target 3200
• Pentair IntelliChlor: 3000-4500 ppm, target 3400
• Jandy AquaPure: 3000-3500 ppm, target 3500

Below the floor, the cell shows Low Salt or No Cell Power and stops generating. Add Solar Salt (NaCl, food-grade or extra-coarse, no anti-caking agent) - never use rock salt or driveway salt. One 40 lb bag in 10,000 gallons raises salinity by approximately 480 ppm.

Check flow through the cell. Pentair IC40 requires 25 GPM minimum. Hayward T-Cell-15 requires 20 GPM. A variable-speed pump set to 1300 RPM overnight may be below the cell's flow switch threshold, generating no chlorine even though the cell is fine. Confirm cell light is steady green during run, not blinking flow-fault.

Step 5 - verify the SWCG output setting

Owners reflexively turn the output down on a cool spring day and forget to bring it back up for July. Confirm the controller is set to at least 50% output for a vinyl pool, 60-70% for plaster, and 100% for an opening week or post-storm shock. If the controller is at 100% and the cell is not generating, check the cell's diagnostic LEDs:

• Hayward AquaRite: press Diagnostic, read salt PPM and cell mV
• Pentair IntelliChlor: press More on the IC40, hold for life remaining + status code
• Jandy AquaPure: read the Ei display, look for E-codes

Step 6 - reverse-cycle and boost shock

If cell is clean, flow is met, salt is correct, CYA / pH are in range, output is at 100%, and you still have zero free chlorine - the pool has a chlorine demand exceeding the cell's max output. Calculate: a Hayward T-Cell-15 puts out 1.45 lb chlorine / 24 hours at 100%. A pool with active algae, high bather load, or fresh fill consumes more than that per day. Boost shock with cal-hypo to 12-15 ppm FC by hand, run pump 24 hours, retest. Once shock burns off to 5 ppm, the cell can hold.

Step 7 - rule out controller failure

If you reach this step, the cell is bad or the controller PCB is bad. Swap the cell with a known-good unit of the same model. If the new cell generates, the old cell was the fault. If not, the controller's H-bridge or power supply has failed - replacement PCBs are available for AquaRite (GLX-PCB-RITE), IntelliChlor (no PCB swap - replace whole unit), AquaPure (R0467500).

References

• Hayward AquaRite Salt Chlorination System Owner's Manual, document IS-AQR-Rev L (2023)
• Pentair IntelliChlor IC Series Installation and User's Guide, document P/N 522414 Rev F
• Jandy AquaPure Ei Series Installation and Operation Manual, document H0480300 Rev D
• ANSI/APSP/ICC-11 2019 - American National Standard for Water Quality in Public Pools and Spas
• CDC Model Aquatic Health Code, 3rd Edition (2023), Section 5.7.3 Disinfection and pH
• Taylor Technologies Pool & Spa Water Chemistry: A Testing and Treatment Guide, 6th Edition