Do you only need to shock if you have CC's?

[rastoma]

I just checked my FC and it was 1.5. CYA=50, PH 7.6, CC=0.

My FC drops about .5 over night and drops almost 2 during the day even in cloudy weather, but water looks perfect, clear and sparkling.

IF CC=0 then doesn't that mean there are no organics that the FC is eating? Do I still need to shock?

 

[dmanb2b]

no need to shock...but you should target a minimum FC of 4...which means you should be raising your FC to at least 6 so that by end of day you will be around 4 and not lower...if you allow it to drop to 1.5 often, you will then develop CC's and need to shock...but every once in a while, no big deal

 

[257WbyMag]

Agree with dmanb2b. Definitely run a higher FC.

 

[chem geek]

In fact, you may find that you lose less chlorine on those cloudy days if you keep the FC level up at the proper level because the chlorine might be getting partially used up fighting nascent algae growth that isn't yet visible. Let us know about your daily chlorine usage after you maintain a 4 ppm FC minimum.

 

[rastoma]

the chlorine might be getting partially used up fighting nascent algae growth that isn't yet visible.

Would that produce CC's?

So having CC's is not the only time to shock?

 

[chem geek]

Algae growth may or may not result in CCs, but it does result in extra chlorine demand. You can distinguish such problems from regular chlorine demand from sunlight by Performing the Overnight FC Loss Test.

As for shocking, this isn't just when CCs are > 0.5 ppm, but also when the overnight FC loss is > 1 ppm or when the water has a lot of organic debris so may be cloudy (that isn't caused by water imbalance as with a high saturation index) or when there is any reason for extra disinfection such as a fecal accident or a dead animal, etc. Usually, though, when a pool is properly maintained you hardly even need to shock.