Shocking a stabilised pool

[Kerryman60]

Hello from Ireland, I maintain two swimming pools for clients. I see a lot of info online about shocking a pool, but usually advising the addition of stabiliser, CYA , AFTER shocking. I keep my pools around CYA 40, but when the CC builds up and I need to shock, the chlorine levels remain high for a very long time, not just, 24 hrs or so, but the days drag on, it seems logical to me, the stabiliser is simply preventing the FC burn off. But , does everyone else have this problem? And please, how to overcome/ understand/work with it?
Also, I don't understand...
If my FC is 4.5 , my CC is 1.2, I slam , as your chart recommends, at 16 ppm , when it breaks apart the molecules, do I suddenly get FC 5.7? Does the CC chlorine become useful again?
Thanks in advance, for your kind replies.

 

[Texas Splash]

Hello! A couple things about your questions. First, here at TFP we generally don't recommend a "shock" in the traditional terms you might hear at the local store. As long as the water is algae-free, we follow that FC/CYA Levels and maintain the proper FC level based on the pool's CYA. But if/when algae does occur, then you already understand we follow the SLAM Process and "maintain" that elevated FC level until we pass all 3 SLAM criteria.

So what can cause a spike in CC? A heavy organic load being process (eliminated) by the chlorine might be one reason. In some areas with limited/low sunlight, an indoor pool, or some with a cover on all the time, that will prevent the sun's UV from oxidizing the CCs. Another reason could be the sanitizing product used. Some people dump a bunch of non-chlorine (MPS) product in the water and this creates a huge spike in CC for quite some time.

For the SLAM Process, we always recommend using liquid chlorine. It's the most reliable, easy to dispense, and quite predictable when trying to maintain the elevated FC level with no side effects. Lastly, we recommend a TF-100 or Taylor K_2006C test kit when doing these tests. It does a good job testing FC and CC separately without confusions. Hope that helps.

 

[mgtfp]

If my FC is 4.5 , my CC is 1.2, I slam , as your chart recommends, at 16 ppm , when it breaks apart the molecules, do I suddenly get FC 5.7? Does the CC chlorine become useful again?
Thanks in advance, for your kind replies.

It gets turned into salt (chloride or Cl^-). With a Salt Water Chlorine Generator, the Cl^- will eventually get turned into FC again, it's a cycle. In a manually chlorinated pool, the salt just accumulates over time.

You add chlorine (via liquid chlorine/bleach, Cal-Hypo, Trichlor or Dichlor). Once it has done it's job killing germs/algae and oxidizing things, or it's been hit by UV, it get's turned into chloride (salt).

 

[Kerryman60]

Thank you both, for prompt and useful replies. I've been reading over TFP articles again, as referred to, regarding slam process,
It was thanks to TFP , back along, that I moved over to liquid chlorine on a regular basis, the articles made clear that the CYA DOES mount up, and fast, despite pool people assuring me it that it is insignificant.
you mentioned "maintain", that's a key word, I'm fighting a difficult battle, as I have many other tasks to perform, other than the pools, so I can only work on the pools every 2-3 days, also , with rental people onsite, I have to fit in with their needs and expectations. Therefore, I can't regularly maintain the correct chlorine levels and it's low by the time I test it. It was easier with the trichlor tabs, as they eroded at a fairly predictable rate. I know that a liquid chlorine pump would feed it in for me, but I don't see these clients spending any more money as they've just put in a new sand filter.
Thanks for your listening ear, and sound advice, I may have to make a case for testing the pool more often. I DO realise the importance of all this, in so many ways, it weighs on me, but my clients don't understand , appreciate , and just don't want to know, especially if the water LOOKS clean and sparkly. Thanks again, for support, and the wonderful service for people like myself.
Kerry.