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Shock For Salt Water Systems


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#1 Dru

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Posted 23 May 2009 - 04:00 AM

Hi,

I have a salt water system and have received conflicting advice regarding shocking my pool. My local pool supply house tells me to use the powdered chlorine shock - BUT - a pool service company that repaired a leaking valve told me to use the 100% production boost button on my control panel and run the pool for 24 hours - essentially producing the same amount of chlorine. I have a Jandy AquaPure salt water system. He seemed to explain that the chlorine in powdered form is actually not good in a salt system as it is higher is calcium I think (I can't remember the exact reason).

Any help/advice/suggestions is appreciated.

#2 ps558

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Posted 23 May 2009 - 07:04 AM

QUOTE (Dru @ May 23 2009, 08:00 AM) <{POST_SNAPBACK}>
Hi,

I have a salt water system and have received conflicting advice regarding shocking my pool. My local pool supply house tells me to use the powdered chlorine shock - BUT - a pool service company that repaired a leaking valve told me to use the 100% production boost button on my control panel and run the pool for 24 hours - essentially producing the same amount of chlorine. I have a Jandy AquaPure salt water system. He seemed to explain that the chlorine in powdered form is actually not good in a salt system as it is higher is calcium I think (I can't remember the exact reason).

Any help/advice/suggestions is appreciated.


The SWG schools all said you can use standard shock to on pool start up. You have to run the pool for 24 hours to get a good salt reading, and if it to low the machine won't produce. I have used cal hypo as well di chlor with no problems

#3 chem geek

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Posted 23 May 2009 - 11:08 AM

If you maintain a Free Chlorine (FC) level (for an SWG) that is at least 4.5% of the Cyanuric Acid (CYA) level, then you should not need to regularly shock your pool. So if you have 80 ppm CYA, which helps protect chlorine from breakdown from sunlight letting you lower your SWG on-time, then maintaining a minimum of 4 ppm FC will prevent algae growth and you should not need to shock unless something unusual happens (e.g. fecal accident, dead animal, much higher bather load with more cloudy water, etc.). Forget the 1-3 ppm FC recommendation with 60-80 ppm CYA that the SWG manufacturers normally recommend; it will often lead to unusual chlorine demand from nascent algae growth. You can combat that with algaecide or phosphate remover at extra cost, or you can just maintain an appropriately higher FC level as indicated.

If you do need to shock your pool for whatever reason, you can use chlorinating liquid or 6% unscented bleach. If you use Cal-Hypo, then the Calcium Hardness (CH) will increase. Using the SWG cell on superchlorinate only wears it out faster. You should NEVER use Dichlor for shocking a pool unless your CYA level is low and you intentionally want to raise it. The following are chemical facts independent of concentration and pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

Richard

#4 jkusmier

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Posted 24 May 2009 - 06:54 PM

Is one even technically "shocking" their pool when boosting SWG output for an extended period of time? I thought shocking implied breakthrough chlorination, i.e. increasing the FC level so quickly that CC is burned out - and I've read the slow FC rise via boosting SWG output won't accomplish that. Or is that BS? Just curious.


#5 chem geek

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Posted 24 May 2009 - 10:20 PM

QUOTE (jkusmier @ May 24 2009, 07:54 PM) <{POST_SNAPBACK}>
Is one even technically "shocking" their pool when boosting SWG output for an extended period of time? I thought shocking implied breakthrough chlorination, i.e. increasing the FC level so quickly that CC is burned out - and I've read the slow FC rise via boosting SWG output won't accomplish that. Or is that BS? Just curious.

It's just BS. Yes, the superchlorinate will raise the chlorine slowly, but it will keep raising it, assuming the SWG is powerful enough. If the CYA level is high, you can get the FC level pretty high, but will be shortening the life of the SWG for no good reason. Shocking with separately added chlorine is the way to go, but is normally not necessary if one keeps the FC at a minimum of at least 4.5% of the CYA level (for SWG pools).

As for getting rid of CC, normal chlorine levels are usually sufficient. All that higher FC levels do is oxidize CC faster. There is no magic number where it "breaks through". The breakpoint chlorination curves usually shown start out with ammonia in the water and then chlorine is added so initially there is no measurable FC and instead CC builds up and then the CC drops and the FC can grow again. In a pool, that's not what happens since there is plenty of excess FC and the CC is continually being oxidized. "Breakpoint" refers to not having enough FC and then you reach a threshold where monochloramine can get oxidized; in a pool with some FC in it, the CC is continually getting oxidized.

Now if the CYA is high and the FC low, then the oxidation reaction can be slow taking hours for monochloramine and for urea taking many days unless the water is exposed to sunlight or the temperature of the water is high (as with spas).

Richard

#6 Jodester

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Posted 03 September 2010 - 04:08 AM

<!--quoteo(post=80149:date=May 24 2009, 07:54 PM:name=jkusmier)--><div class='quotetop'>QUOTE (jkusmier @ May 24 2009, 07:54 PM) <a href="index.php?act=findpost&pid=80149"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->Is one even technically "shocking" their pool when boosting SWG output for an extended period of time? I thought shocking implied breakthrough chlorination, i.e. increasing the FC level so quickly that CC is burned out - and I've read the slow FC rise via boosting SWG output won't accomplish that. Or is that BS? Just curious.<!--QuoteEnd--></div><!--QuoteEEnd-->
It's just BS. Yes, the superchlorinate will raise the chlorine slowly, but it will keep raising it, assuming the SWG is powerful enough. If the CYA level is high, you can get the FC level pretty high, but will be shortening the life of the SWG for no good reason. Shocking with separately added chlorine is the way to go, but is normally not necessary if one keeps the FC at a minimum of at least 4.5% of the CYA level (for SWG pools).

As for getting rid of CC, normal chlorine levels are usually sufficient. All that higher FC levels do is oxidize CC faster. There is no magic number where it "breaks through". The breakpoint chlorination curves usually shown start out with ammonia in the water and then chlorine is added so initially there is no measurable FC and instead CC builds up and then the CC drops and the FC can grow again. In a pool, that's not what happens since there is plenty of excess FC and the CC is continually being oxidized. "Breakpoint" refers to not having enough FC and then you reach a threshold where monochloramine can get oxidized; in a pool with some FC in it, the CC is continually getting oxidized.

Now if the CYA is high and the FC low, then the oxidation reaction can be slow taking hours for monochloramine and for urea taking many days unless the water is exposed to sunlight or the temperature of the water is high (as with spas).

Richard


I just converted to a salt system myself. I just want to make sure I understand correctly -- you're saying that we should really try not to ever use the superchlor function on the salt cell?? And that if we need to shock, we should only use liquid chlorine?? I'm stunned -- the main reason, after all my research, that I decided to switch to salt was that I would never have to handle noxious chlorine ever again! The only reason I was considering adding powdered shock (Leslie's PowerPowder Pro) was because the CYA is low (since the pool was just filled). I was then planning on giving away all my chlorine products!

#7 Pool Clown

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Posted 03 September 2010 - 06:52 AM

I'm stunned -- the main reason, after all my research, that I decided to switch to salt was that I would never have to handle noxious chlorine ever again! The only reason I was considering adding powdered shock (Leslie's PowerPowder Pro) was because the CYA is low (since the pool was just filled). I was then planning on giving away all my chlorine products!

As Richard said in the first sentence of his first post here,(in a nut shell) If you maintain your chems properly, there is no need to shock. If you want to raise your CYA, you need not piggyback it on chlorine. You can get CYA by itself (less toxic).

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#8 Jodester

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Posted 03 September 2010 - 07:48 AM

Okay -- I understand. So I should bring my CYA levels up to normal first, and if I'm still not seeing adequate chlorine, I can take it from there. Right now, the generator has been running at 100% with the filter on for about 4.5 hours, and the chlorine levels are still barely being picked up by my liquid test kit. I did a test right at the return and I do get a higher reading there, so I know chlorine is being produced, just not holding.

#9 Pool Clown

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Posted 03 September 2010 - 09:11 AM

A cool trick is to loosen the downstream union of the cell, while its running, just enough to make it leak a small stream, and take your water sample from there to check for Cell operation.

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#10 AFiremanFirst

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Posted 03 September 2010 - 04:46 PM

Dru
Chemgeek and pool clown are 2 of the most respected guys on this forum. I'm analytical and can't hold a candle to these guys. They know all that you'd ever care to know about chemical chemistry. In laymans terms. Destroying CC by "superchlorinating" at 30 times your FC is a little bit of a stretch. CC is seldom seen in an outdoor pool. But they are both right. CYA first, then FC. Boosting is fine. As they have taught me... Your chlorinator operates for 3 hrs (roughly depending on your manufacture). 100% just means a 100% of 3 hrs vs 40% etc... wanna run it 2 hrs at 100% fine, 4 hours at 50% is the same. You won't damage your SWG or save it by going 50%. However if you don't have CYA (sunscreen for chlorine) you can generate as much chlorine as you want, and it won't matter, as it's a gas and will evaporate! BTW 30-50ppm of CYA is plenty, more and you need to adjust for chlorine that is tied up by CYA... More on this later

#11 chem geek

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Posted 03 September 2010 - 05:21 PM

However if you don't have CYA (sunscreen for chlorine) you can generate as much chlorine as you want, and it won't matter, as it's a gas and will evaporate!

Thanks for the compliment and you got this almost perfect. The only thing not quite right is that it's not that chlorine evaporates, but rather that it breaks down (turns into salt -- chloride) from the UV in sunlight. CYA prevents that to a large degree, not only from shielding lower depths, but from combining with chlorine to produce a more stable compound more resistant to such breakdown. Unfortunately this chlorine+CYA compound essentially doesn't disinfect nor kill algae.

#12 Pool Clown

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Posted 03 September 2010 - 05:39 PM

I too thank you for the sentiment, but i fell asleep during chemistry. Don't trust me with the water. I'm more of the mechanical type. So if it's broke, leaks, or the lights don't come on, i'll take a crack at it.

However, I like the CYA up around 70 for the generators, BTW thats CHLORINE generator not SWG (Salt water generator).

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#13 waterbear

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Posted 03 September 2010 - 07:22 PM

, BTW thats CHLORINE generator not SWG (Salt water generator).


To be technical it's a SWCG (salt water chlorine generator). Posted ImagePosted Image (just messin' with ya', Pool Clown!)

On a newly started SWCG it is often necessary to manually raise the FC to 'shock level' and then the unit take over chlorine production but you do need to have a proper CYA level first. Good rule of thumb is to put it at the top of the manufacturer's recommended range (usually 80 of 100 ppm). Until then you will possibly have to manually supplement the chlorine by manual addition. IMHO, sodium hypochlorte (liquid chlorine or laundry bleach) is the best to use since it has the fewest side effects and is essentiall what your SWCG is producing.



So if it's broke, leaks, or the lights don't come on, i'll take a crack at it.


Then get on over to my house! I need to replace a pump motor, find the leak in my spa. and replace a few valves. I'm more the water chemistry type! I don't interface well with the mechanical!
I've tested more water than I ever care to think about!
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#14 Pool Clown

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Posted 03 September 2010 - 08:51 PM

Then get on over to my house! I need to replace a pump motor, find the leak in my spa. and replace a few valves.


Sorry, but i used up the last of my C-4 on the fourth... B)

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#15 waterbear

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Posted 03 September 2010 - 08:56 PM


Then get on over to my house! I need to replace a pump motor, find the leak in my spa. and replace a few valves.


Sorry, but i used up the last of my C-4 on the fourth... B)


At this point it might be the best solution! Isn't it always the case that everyting breaks at once, this summer I lost an actuator because the valve sprung a leak into it, had to replace a check valve, developed a leak in the attached spa that still is eluding me, and my pump motor died two weeks ago. The green has started but I just have not had the time to deal with it yet.Posted Image (changing out a motor is probably my least favorite thing to do and I am seriously considering paying someone to do it for me!)
I've tested more water than I ever care to think about!
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#16 Pool Clown

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Posted 04 September 2010 - 08:22 AM

(changing out a motor is probably my least favorite thing to do and I am seriously considering paying someone to do it for me!)


I reply noting your level of ability with,

WAAAAAA!!!!!!!!

P.S. you have a love letter waiting for you, from your buddy Dale, here

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