Shock

[Bobbyk]

I want to shock my 28k IG SW pool.

I heard I would need to add enough shock to raise the Chlorine level 10 times the level of my combined Chlorine. The shock I have is calcium hypochlorite.

My Combined Chlorine level is 3.4 ppm. Therefore, I am aiming to add enough shock to obtain 34 ppm Chlorine.

I do not know how much shock to add.

I could calculate the amount, but I do not know how much shock I would need to add to raise my Chlorine level a given amount.

Does anyone know?

 

[dbrown199]

Bobby, you need to know what your CYA level is. With out that your swinging in the dark. Pease ckeck out pool school to get a better grip on SHOCKING. Also look at the pool calc. on the front page left side. Good luck.

 

[Bobbyk]

My CYA is 55. What does that have to do with how much shock I need to add?

 

[Ohm_Boy]

While CYA (stabilizer) makes the chlorine last longer in sunshine/UV, you don't get something for nothing... the tradeoff is that it reduces the effectiveness of chlorine. Consequently, as the CYA goes up, the pool requires higher and higher levels of chlorine.

Shocking is about reaching a higher chlorine level, but the part that the pool stores leave out is that the effective level is dependent upon CYA.
A long time ago, a fellow named Ben Powell found out the relationship between the two, and determined through his pool business the best numbers for free chlorine and shocking levels, which he published on his poolforums site.
There is a chart on this forum, based upon that original work and further developed by Chem_Geek, which shows the chlorine levels needed at various CYA levels.
category/pool-school/chlorine_cya_chart_shock

With a CYA level of 55, you should probably shock to about 22 ppm. You will want to check your PH beforehand as well, as chlorine is more effective around 7.2 ph.

 

[Bobbyk]

Thank you for the explanation and additional info. I printed the chart. Then, I assume you would recommend that I ignore what I heard about the proper level of shock being enough shock to raise the Chlorine level 10 times the level of the Combined Chlorine?

Also, any idea how much shock (calcium hypochlorite) it takes to raise a given amount of water a given amount (say 10k gals 10 ppm)?

 

[JasonLion]

You can use my Pool Calculator, see the link in my signature, to figure out how much of a chemical you need to hit a target level.

The story about needing 10 times the CC level of chlorine is just wrong. There is a rule like that for ammonia. But none of that really applies here. You don't know what else is in the water that you will need chlorine to oxidize. So the total amount of chlorine might be higher than you think. Still, you should only add chlorine up to shock level at one time, wait for the FC level to fall and then add more chlorine. That process is called shocking the pool.

For directions on shocking the pool see this article.

 

[dbrown199]

Thank you Jason you can say it better than me. :lol:

 

[Bobbyk]

Thanks. Should I shock, or use the Phosphate Remover 1st? Does it matter?

 

[JasonLion]

I would shock first and skip the phosphate remover completely. Phosphate removers are almost always a waste of money.

Even if you believe in phosphate remover, you should shock first. The instructions for PhosFree say "DON’T add to a pool with live algae or a pool that is not clean or balanced".

 

[Bobbyk]

Okay. Thanks. Well, I'm pretty sure that Phosphates are disrupting the ecosystem in my pool, so I hope the Chem I ordered will eliminate them. (They've been building up for 12 years now.)

 

[chem geek]

Pretty much the same conversation occurred in this thread. I agree that you should shock first since it should take care of the problem and that phosphate removers are a last resort, but I said it was up to you.

 

[Guest]

I concur, don't waste your time or money on the phosphate removers.