"shock" Vs. Just Adding Chemicals

[Greenhorn]

Well, I've probably read 20 hours worth of info on this site so far. One thing I've read that I'm not sure about is the term "shock". Does it mean to add a higher dose of chlorine as opposed to just adding your normal daily use?

One other thing. Is it just me or does anyone else see a very low amount of users viewing this forum? I read chem geeks advice on getting rid of the floating ad while viewing, maybe that's why I'm not seeing more responses?

Mike

[Spanky]

Shocking means to raise FC to about 10ppm. This is to rapidly oxidize any stubborn organics or other contaminants which would not be possible at normal sanitizer levels. This shuld be done every week or every 2 weeks (depending on bather load)

To shock, add enough liquid chlorine (bleach) to raise FC to 10ppm the run the spa uncovered in sunlight for about an hour. The FC should return to normal. If it's still high run another 1/2 hr then recheck. DO NOT allow bathers into the spa untill the chlorine level is back to normal (below 4ppm)

NOTE Even saltwater spas, which constantly generate chlorine, have to be manually shocked. DO NOT confuse this with "boost mode" which is designed to rapidly replace FC after high bather demand. It is not the same as shocking.

[chem geek]

Some people using the Dichlor-then-bleach method don't ever need to shock their spa. This is also true when using chlorinating liquid or bleach for pools. So long as one adds enough chlorine after each soak in a spa, then it may be enough to get rid of the bather waste and keep the water clear. As you've pointed out in another post on another recent thread, the Dichlor-only method that builds up CYA over time is what causes problems when the CYA builds up and shocking is a way to try and make up for that by boosting the FC level, but it's not really the best solution. It's better to not build up the CYA in the first place.

[SpeedStar]

With the ACE SWCG would I be better off to shock with MPS or Dichlor? And with this system am I still targeting 10PPM to shock? It is my understanding that MPS will not drive up CYA levels. Thanks.

[MPurcell]

Shock level depends on the amount of CYA. At zero CYA, shock level is 10 ppm. At 30 ppm of CYA, shock level is 12 ppm. You do need CYA in the tub if you use chlorine as the sanitizer. You probably don't want the CYA in the tub to go above about 30 to 40 ppm, although I am not really sure if the SWCG changes those numbers. Please see the sticky post above on the Dichlor/bleach Method. MPS does not add CYA, but it is expensive, and does add other dissolved solids. I would recommend using household bleach as an oxidizer and/or source of chlorine when you need to shock. Just be sure you don't use splashless bleach or scented bleach. Just get straight 8.25% bleach from the grocery store or Walmart. You can use the Pool Calculator to determine how much bleach to add to achieve a certain free chlorine ppm.

[SpeedStar]

I have my CYA level at around 35 now by using the SWCG (current output setting at 3-4 range) and supplementing with Dichlor after each soak. pH 7.5, TA 60, Borates added, CH 50 per Hotsprings ACE target. Now I will switch to Clorox 8.25% concentrated regular bleach after each soak. Per the TFP calculator, I am thinking I should add between 1 to 2 fl oz. of 8.25% bleach after each soak to replace the normal .2 - .4 oz of Dichlor that I was using. Then as CYA levels drop cycle back to Dichlor?  Is there any problem with pouring the bleach in and closing the cover or does it need to sit open for a while after using and dosing the bleach?

So for the bleach shock with CYA level maintained 30-40 range, I add 5-6fl oz of bleach to increase FC to 10-11ppm range and run pumps for an hour or so to oxidize. Are you saying the FC should drop back to 3ppm range within that hour or will it take until the next day or so to come back down? If it does not come down to the 3ppm range in a few hours, can I neutralize the added chlorine level back down with 3% hydrogen peroxide if we want to use the spa at that point or do you need to wait for it to return to normal levels on its own to fully benefit from the shock? Thank you for the help. This is all new to me and this forum has been a great resource.

[MPurcell]

I use bromine, so I don't have experience with a chlorine tub, but I often put the lid on right after adding the bleach. According to what I've read, it is better to leave the lid off a little while to allow off gassing.

With a CYA of 30, shock level is 12 ppm, and with a CYA of 40, shock level is 16 ppm, for equivalent effective disinfecting chlorine amounts. It will usually take longer than one or two hours for the chlorine level to come down. The actual time depends on how much material that needs to be oxidized is in the water. If there is a lot, the chlorine can come down rather quickly.

If a tub is managed correctly, it should not be necessary to take the chlorine up to shock level. If you keep your water chemistry balanced, and the chlorine level always above 2 ppm (for 30 CYA) or 3 ppm (for 40 CYA), and if you add enough bleach after each soak to neutralize the bather waste, then you should never have to shock.

I use bromine, but the principal is the same. I have only shocked twice in the last 4-1/2 months, and one of those was to test the bromine demand of the tub.

[SpeedStar]

Thanks for the clarification on shock. I thought it was a requirement. I am learning a lot here.