Is a drop of 3.5FC normal for a rainy day?

[joecoyle]

Hi

Yesterday my F.C. was at 5 so I bumped it up to 7 as per the chart with 15% bleach.

Then it rained for the rest of the day.

Tested again today and it’s down to 4.5. Is a 3.5 drop normal after rain? Or are there some nasties consuming my chlorine??

pH 7.3
CC 0
TA 75
Cya 50/60
Temp 18C

I’ve never noticed a big drop before

Anyway I’ve brought it back to 7

Cheers
Joe

 

[SemperFly]

You only lost 2.5ppm, not 3.5 (7.0-4.5), but you could always do an OCLT to verify whether or not organic material is consuming your fc.

 

[joecoyle]

Oops. It’s been a long day.