Shock the pool after replace 2/3 water?

[Guest]

In order to reduce CYA, I replaced 2/3 of my pool (in one time) with tap water.

PoolSchool says "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 shock the pool when the FC level falls significantly, as it often does after a major storm or large swim party."

Before replacing water, FC 4-5, CYA 100-110
After, FC 0, CYA 40-50.
Then I bring FC up to 5 by Clorox.

In my case, do I need to shock my pool?
Another question, suppose I have to shock, after
"A:CC is 0.5 or lower; B:An overnight FC loss test shows a loss of 1.0 ppm or less; C:And the water is clear."
is there anything else need to do to lower FC, or just let it go down by itself?

Thank you

 

[Richard320]

I reviewed your other thread. Is the water still clear?

If so, I'd run it up to shock level for a day, then do the overnight test. If it passes (and it should), you can relax and the chlorine level will drop all by itself when sunlight hits it, probably 2 or 3 ppm per day. It is safe to swim up to shock level, so if the pH is good and the temperature is bearable, have a swim!

 

[Guest]

I reviewed your other thread. Is the water still clear?

If so, I'd run it up to shock level for a day, then do the overnight test. If it passes (and it should), you can relax and the chlorine level will drop all by itself when sunlight hits it, probably 2 or 3 ppm per day. It is safe to swim up to shock level, so if the pH is good and the temperature is bearable, have a swim!

Thank you so much for the prompt reply, Richard!

The water looks quite good (as before )
Now the FC in my pool is 4.8-5 (after sunset), CC <=0.2 CYA 40-50, PH 8, TA 100, CH 250
Tomorrow morning, I will do the overnight test. If it pass (<1), do you think I still need to shock my pool?

Also, I will get some muriatic acid tomorrow to lower the PH.

 

[linen]

Just a note...no need to do the 25 ml sample for FC and CC, the 10 ml sample amount will give you enough resolution (0.5 ppm) and will save you reagents.

 

[Guest]

Just a note...no need to do the 25 ml sample for FC and CC, the 10 ml sample amount will give you enough resolution (0.5 ppm) and will save you reagents.

Even for overnight test? I though overnight test requires fine precision.

 

[linen]

0.5 ppm is plenty since you are looking for a OCLT of 1 ppm or less.

 

[Guest]

0.5 ppm is plenty since you are looking for a OCLT of 1 ppm or less.

Got it. Thank you :-D
Do I need to shock my pool if OCLT <1ppm?

 

[Richard320]

0.5 ppm is plenty since you are looking for a OCLT of 1 ppm or less.

Got it. Thank you :-D
Do I need to shock my pool if OCLT <1ppm?

Straight off Linen's signature: 1. CC is less than 0.5 ppm, 2. An OCLT shows a loss of 1.0 ppm or less and, 3. The water is crystal clear.

If it passes, you're done.

 

[Guest]

0.5 ppm is plenty since you are looking for a OCLT of 1 ppm or less.

Got it. Thank you :-D
Do I need to shock my pool if OCLT <1ppm?

Straight off Linen's signature: 1. CC is less than 0.5 ppm, 2. An OCLT shows a loss of 1.0 ppm or less and, 3. The water is crystal clear.

If it passes, you're done.

Sorry, as a newbie, I am a little confused.
Those 3 criteria are the condition of "stopping" Shocking Process.
But if my pool meets them before shocking (i.e., low FC), do I still need to "begin" shocking process by raising FC?

 

[linen]

Since your water is clear, and your CC<0.5 ppm, then you have no reason to do the shocking process. However given your pools history, as Richard320 said, I too would recommend doing the OCLT, and I would raise you FC up to shock level when doing it...just to be sure.

 

[Guest]

Since your water is clear, and your CC<0.5 ppm, then you have no reason to do the shocking process. However given your pools history, I would do the OCLT, and I would raise you FC up to shock level when doing it...just to be sure.

I see. Thank you, linen

 

[duraleigh]

All the discussion about shock has disregarded your one parameter which is out of line. Get your pH down to about 7.5 sooner rather than later.