SLAM time again... How important is low CYA high PH before starting shock?

ggoodwinj3

Member
Jan 8, 2015
22
Fuquay Varina, NC
Once again - I outsmarted myself thinking I would get away with opening the pool before the swamp took hold. A few warm days in February and March took care of that.

Current chemistry:
Chlorine: 0
PH: 8+ adding 8 drops of acid demand bring it back into range - 9 drops instantly turn it yellow and put it below 7.0
CYA: 30 or less
TA: - 60
Frogs: 5-6 that Ive seen

I'm off to Tractor Supply for Muriatric acid.

The muriatric is gonna lower the CYA even further. Is there a concern if I ignore the TA/CYA and get the SLAM underway?
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
The muriatic acid should have no bearing on your CYA (stabilizer), only lowering the pH and TA. So definitely lower the pH right away since it's so high. Once you get it down to the lower 7s, you can increase your FC with regular bleach. Make sure you have at least 20ppm of CYA, 30 is ideal. Your SLAM/Shock level will be:
FC of 10 for a CYA of 20
FC of 12 for a CYA of 30
Remember to follow everything listed on the SLAM page (link below) and don't stop until you pass all 3 SLAM criteria. AFTER you pass the SLAM, remember to increase your CYA to at last 70 to better support your SWG. Good luck.
 

ggoodwinj3

Member
Jan 8, 2015
22
Fuquay Varina, NC
The muriatic acid should have no bearing on your CYA (stabilizer), only lowering the pH and TA. So definitely lower the pH right away since it's so high. Once you get it down to the lower 7s, you can increase your FC with regular bleach. Make sure you have at least 20ppm of CYA, 30 is ideal. Your SLAM/Shock level will be:
FC of 10 for a CYA of 20
FC of 12 for a CYA of 30
Remember to follow everything listed on the SLAM page (link below) and don't stop until you pass all 3 SLAM criteria. AFTER you pass the SLAM, remember to increase your CYA to at last 70 to better support your SWG. Good luck.
Doh! I meant TA not CYA.

Thanks for the quick response! This my 3rd SLAM - the only year I didn't have to do it was when I left the filter running all winter. Of course Mother Nature brought the coldest NC winter in years...LOL!

- - - Updated - - -

Getting your PH to the low 7's will help your chlorine work better.
Hi Ned,

I'm down in Fuquay.

Thanks for the quick reply.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,395
Franklin, NC
Getting your PH to the low 7's will help your chlorine work better.
While this is technically true for water with nothing else in it, once you add CYA to the water the effects of the pH are "buffered". Here is Chem Geek's explination:

With no CYA in the water, going from a pH of 7.5 to 8.0 lowers the active chlorine (hypochlorous acid) level by roughly 50%. With CYA in the water, not just at 30 ppm as in what I showed in the graphs bug higher levels as well, the same pH change only has the active chlorine level drop by 15%. So you can generally ignore the pH effect on chlorine. Cyanuric Acid is a buffer for hypochlorous acid so resists changes in the active chlorine concentration.
So, with CYA in the water you can ignore the pH as far as effectiveness of the chlorine goes.

We recommend pH in the low 7's to start a SLAM not because the chlorine is more effective, but because once the FC goes above 10 you will not be able to accurately test the pH. With all the brushing, pump running and other aeration during the SLAM we know the pH will rise, so start at the lower end of recomended.
 

ned8377

LifeTime Supporter
Apr 30, 2015
250
Wake Forest, NC
Thanks Tim, I didn't know that CYA had that affect on PH but makes sense. There you go, learned something new again.

Hello ggoodwinj3,

TFP has been a life saver for me. I don't ever go to pool stores around here anymore. Got tired of being jerked around and being told 3 different things at 3 different stores.
 

ggoodwinj3

Member
Jan 8, 2015
22
Fuquay Varina, NC
If after lowering the pH you find the TA took a dive too much, just have some baking soda available to keep it over 50 at least. After your SLAM you can readdress pH and TA to see how best to keep them stable.
Ever since I got the salt cell installed - I get the water balanced in the spring and almost never need to do much more than a fine tune once every week or 2.