FC not dropping after shock


New member
May 7, 2020
Dover, MA
Long story short -- let my 34K gal SWG pool FC get too low for too long (I had an inadequate amount of CYA in water and was constantly using whatever FC was generated) and what I thought had been pollen at the bottom of the pool was actually algae. I SLAM'ed it (first time SLAM) one rainy week late June/early July and was amazed at the results. I put in 15 gal of chlorine over 2 days, and the pool looked amazing. FC took a long time to drift down, so SWG was off nearly a week.

Fast forward a month, and after a hot, high-use weekend it was looking a bit cloudy and greenish, so worried about algae again, I put in 3 bags of granular shock. I forgot to keep the pump running all night but turned it on first thing, brushed the pool, and ran the pump all day. We didn't swim that day, obviously, but it was full sun and hot so I expected the FC to decrease quickly. Monday FC was 10, and I turned off the SWG, pool was in full sun about 6 hours. Tuesday also sunny and hot (2 days post shock), the pool looks great but FC is still 9.5 and we desperately want to swim! Why isn't FC drifting down??

Sun eve - 3 bags granular shock
Tuesday readings
FC 9.5
CC 0
pH 7.8
Alkalinity 120
CH 300
CYA 80


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Jul 16, 2012
Central MD
Give yourself a little more time and testing to check daily FC losses. Yes, your FC should go down daily and it will. Though as Marty said, your FC is not high at all. Just slightly above your ideal range. Completely harmless, except to algae.