How to Shock a high ph Salt Pool with Bleach

[AkronOhioPoolOwner]

Converted to a Salt Pool in spring of 2009 when a new liner was installed.
Pool is 24x36 and about 19,800 gallons with radius corners, corner steps, 2 jets, 1 skimmer plus bottom drain return. the chlorine generator seems to do a good job at keeping pool clear with low level of chlorine in pool so have not felt the need to shock the pool. I have been trying to keep the pool water chemical free except for adding a small amount of stabilizer. In 2009 and 2010 I dissolved granular stabilizer by placing it in an old sock and hanging it in the pool. Over the winter I had a plumbing leak and lost 2/3 of the water so most of the granular stabilizer is probably gone with the lost water. I was told that granular stabilizer could be bad for the chlorine generator so this spring I added 2 gallons of liquid stabilizer and all seems to be fine. The ph seems to run rather high (usually it is at about 8.0) so I add 1/2 gal of muratic acid from time to time to bring the ph down but it rather quickly comes back up. I read in the Pool Solutions Tips that a high ph may be OK as long as it does not get too high so perhaps adding acid is a waste of time? The total alkalinity has always been rather high (200ppm+) as well.
With small children now using the pool I feel I should start shocking after heavy use.
How much household bleach should be added to effectively shock the pool and how often should this be done. Should the chlorine generator be turned off when shocking and if so should I wait until the chlorine level comes back down before turning it back on?

[aylad]

Hi, and welcome to the forum!

You are right that most of your stabilizer probably went out with the water, but as far as granulated/liquid CYA, there's really no difference once it gets into the water--granular is no worse for SWCG than liquid. In fact, keeping an adequate amount of CYA in the water is important to help your unit's cell life...The SWCG gurus on this forum have said that keeping the CYA levels lower than your unit's manufacturer recommendations can actually shorten the cell life. Most SWCG's want 80-100 ppm of CYA, so you really need to check the manual for your unit and adjust yours accordingly.

It is normal for the pH to rise as a result of running the SWCG--that's because of the way it works. One of the products of the conversion from salt to chlorine is the release of hydrogen bubbles, which are acidic--and as they come to the surface and evaporate, your pool is losing acidity, therefore the pH is increasing. If you'll lower your TA to the 70-80 range, and then only add acid to drop the pH to 7.6, I think you'll find that your pH is a lot more stable and you won't have to use as much acid. You can lower your alk by this method; http://www.poolforum.com/pf2/showthread.php?t=191

There is really no need to shock the pool unless you're having an onset of cloudiness, see an excessive amount of chlorine use, or have a suspicion that there's a lot of goo in the pool that needs to be sanitized, i.e. lots of small kids, dogs, hurricane, etc (not that you have a lot of hurricanes in Ohio but we do get them down here in Louisiana!). One easy way to see if it needs to be shocked is if you test the chlorine at night after the sun is off the pool, and then test again in the morning before the sun hits the pool. If you lose more than 1 ppm of chlorine in that time, then the pool needs to be shocked. Also, if you test at any given point in the day and your CC is more than 1 ppm, then it's a good idea to shock. How high to take your chlorine level when you shock depends on your CYA level--here's the table: http://www.poolsolutions.com/gd/best-guess-swimming-pool-chlorine-chart.html#a. I don't think it's necessary to turn the SWCG off when shocking with bleach--the worst case scenario is that you raise the chlorine a little higher than you intended, but that won't hurt anythig--it may just take a little longer for it to come back down to normal after the shock--it's really up to you. In a 19,800 gallon pool, each gallon of 6% bleach will raise the FC by 3 ppm, so you can use that as a guide to decide how much to add. Some people pour it directly into the skimmer, and some people pour it slowly into the return stream. Either way will help disperse the bleach into the pool. Just be careful not to splash on the side of the pool, or in your eyes or clothes. (Wear old clothes--even after 9 years of pouring bleach, I STILL splash it sometimes!). It's usually the most efficient if you'll add it at night, after all the swimmers are out of the pool, so that it has the whole night to work on goo in the water without interference from the sun.

Hope this helps!

[AkronOhioPoolOwner]

Thank you so much for your help.
I will give lowering TA a yeoman's try.

[waterbear]

As Aylad said, the main causes of fast pH rise in a salt pool are:
CYA too low causing the cell to be on too much which aerates the wate which causes CO2 to outgass which causes the pH to rise.
TA too high which over carbonates the water which means faster outgassing of CO2 which means faster pH rise. (Yours is WAY TOO HIGH for a salt pool. Get it down to abougt 70 ppm! It will solve a lot of your problem.)
pH dropped to0 low which converts more bicarbonate (TA) into CO2 (just like putting vinegar on baking soda) which outgasses which causes pH to rise.

Finally, If you keep your FC at about 5% of your CYA level you will probably never need to shock a salt pool. However, if there is a fecal accident or they are urinating in the pool then that is a different matter.
If your testing is showing persistent combined chlorine then a better plan would be to run your FC a bit higher than you are.