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OCLT Tracker

Overnight Chlorine Loss Test — log sunset & sunrise FC and auto-calc the loss.

Date

Sunset FC (ppm)

Sunrise FC (ppm)

CC (ppm) (optional)

Notes (optional)

0 saved

Pass criteria (typical guidance):

FC loss ≤ 1.0 ppm overnight
CC ≤ 0.5 ppm
Water is clear

Tip: Do the sunset test after the sun is off the pool and after circulating ~30 minutes.

History

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Date	Sunset FC	Sunrise FC	Loss	CC	Status	Notes

Understanding the Overnight Chlorine Loss Test (OCLT)

The Overnight Chlorine Loss Test is one of the best ways to determine whether algae or another organic contaminant is still consuming chlorine in your swimming pool. Because sunlight destroys chlorine during the day, the test is performed overnight when the sun is no longer affecting chlorine levels.

How the Test Works

Test and record your Free Chlorine after sunset, allow the pump to circulate overnight, then test again before sunrise. The difference between the two readings is your overnight chlorine loss.

Passing the OCLT

Free Chlorine loss is 1.0 ppm or less.
Combined Chlorine (CC) is 0.5 ppm or lower.
The pool water is crystal clear.

Why It Matters

If you lose more than 1 ppm of Free Chlorine overnight, something in the water is still consuming sanitizer. Continue the SLAM Process until all three passing conditions are met.

Important Notes

Perform the evening test after the sun is off the pool.
Run the circulation system overnight.
Take the morning sample before direct sunlight reaches the pool.
Use the same accurate test kit for both readings.

Poolside quick-reference Splash Sheets

Grab-and-go cheat sheets that pair with these calculators for the pool deck.

View Splash Sheets