What is your FC at when you shock?


Well-known member
May 31, 2012
Allentown, PA
So I read this in pool school...
"Shocking the pool will eliminate algae, combined chlorine (CC), and any other organic contamination. If you have algae, or the CC level is above 0.5, or the free chlorine (FC) level is zero, you should shock the pool. Many people also like to s--hock the pool when the FC level falls significantly, as it often does after a major storm or large swim party. This is done even if FC doesn't get all the way to zero, just to be sure everything is all right. If you are maintaining proper FC levels there is no need to shock weekly, or on any other regular schedule."
Here is my questions:
If everything looks good, but you notice that the FC has gone down to 2ppm should you shock or just add the normal amount of bleach to bring it to 3-7ppm FC level? Or if you have gone over 8 weeks without shocking is that okay, or would it be a good time to shock the pool if the FC drops to 2ppm? I guess I'm looking for some opinions and kind of what your shock schedule looks like using the BBB. Thanks


LifeTime Supporter
TFP Expert
Feb 23, 2008
Denton, TX
The only reason to shock is if:

1.) your CC is greater than 0.5 ppm
2.) you lose more than 1 ppm of FC overnight
3.) the water looks dirty and you think that this is due to organic contaminants (algae, swimmer waste, etc.)

Routine shocking is not indicated. There are many, many people here at TFP that have never once needed to shock their pool.


LifeTime Supporter
TFP Expert
Jan 6, 2010
San Dimas, CA (LA County)
What is this thing called shock?

I've never done it.

I've had FC dip below minimum a time or two, but if the pool is generally kept balanced, one day missed isn't going to make it turn green. That would be equivalent to saying one day without vegetables will make you come down with rickets and scurvy. If I let it dip, I bring it back up to normal and maybe a splash of bleach extra.

If you test your water regularly and keep pH in range and FC above minimum for your CYA level, you may never have to do the shock process. Even if you have life happen and neglect it for a day or two.


LifeTime Supporter
TFP Expert
May 10, 2010
SW Louisiana
1, normal depends on how much CYA you have in the water, if you have the suggested 40 ppm of CYA, then your acceptable minimum FC is 3 ppm and target should be 5 ppm, if you drop to 2 (assuming it is not for a long duration), you should return to your target level and watch for signs of algae (cloudy water, excessive chlorine use, etc.), only shock if you show signs of algae.

2, If everything is in balance then there is no reason to shock ever, many people here go years without shocking, then only shock when some major event happens (storm blows lots of junk into the pool, pump failure keeps them from adding chlorine for several days, etc)

3, Shock only when there is a sign of algae in the pool, and attempt to keep minimum levels of FC and good water balance overall so this is extremely rare. Pool stores have convinced everyone shocking is normal, much like Microsoft has convinced everyone that computer just crash at random.


LifeTime Supporter
TFP Expert
Jun 5, 2012
DFW, Texas

Agree with Richard...add enough bleach to bring your FC to within the target levels (maybe the upper bound of that range for a couple of days) according to your pool's CYA.

You should only shock if you have visible signs of algae or other evidence of organic contamination (e.g., human/animal waste, a dead critter) or test results that meet the criteria that 257WbyMag posted. Never base the need to shock on an arbitrary timetable.

When the day comes that you have a need to shock, here is the process: Shock Your Pool. As for the target shock FC, click the Chlorine/CYA Chart link in my sig,