Combined chlorine and ammonia problem

[seanmahan]

We recently opened our pool and are having a problem with combined chlorine and ammonia. I have a 33,000 gal vinyl in ground pool (fc 0.5, cc 5, pH 7.2, TA 140, CH 160, CYA 0). I can't get the FC level to budge above 0.5-1.0 and the combined chlorine is reading 5+. Based on discussions on this site I decided to check the ammonia level which reads about 6.0-8.0 (I admit to letting the pool go over the winter and opening it late). To get rid of ammonia it has been suggested to shock to 10x the ammonia reading, so in my case 60-80 ppm. In a 33,000 gal that's a lot of chlorine!

A coworker told me that non-chlorine shock (specifically potassium peroxymonosulfate) can be used to destroy ammonia. Is this true? If so, are there any drawbacks? It might be preferable because my understanding is that it will start destroying some ammonia without having to shock to the 60-80 ppm breakpoint and it would be safe to swim shortly after application (which is important since company is coming for the holiday weekend.

I apologize if this doesn't make any sense as I'm still trying to get my head around the chemistry. Any help and input is appreciated.

Thanks,
Sean M.

 

[RobbieH]

Do you have any organic material in your pool? I'm not talking algae, but foreign material such as leaves.

 

[Bama Rambler]

The breakpoint myth is just that, a myth. While it takes that amount of chlorine to break it down you don't have to try and add it all at once.

Without any CYA in there you need to add enough chlorine to get to 10 ppm FC and test and add what's needed to get back to 10 as often as every hour. The only reason to wait an hour is to allow the water to mix. You will need to have lots of chlorine on hand to make this go as quickly as possible.

 

[RobbieH]

Agreed, it's going to suck chlorine for a while! You might be surprised how much chlorine you are adding each hour.

 

[seanmahan]

Do you have any organic material in your pool? I'm not talking algae, but foreign material such as leaves.

No, the pool is clean and the water looks pretty clear although you can tell it's a little milky when looking at the deep end.

Thanks,
Sean M.

 

[RobbieH]

Sounds like you just need to follow the shock process as outlined here:
pool-school/shocking_your_pool

Don't let a friend or a pool store talk you into a bag of shock as a total solution.

 

[JasonLion]

Non-chlorine shock will work just fine, but it will end up costing more than the chlorine required to do the same job will cost. The amount of chlorine required is 8 to 10 times the ammonia level, but remember that you can also lose chlorine to sunlight, so you might need more than that if you do it during the day.

 

[seanmahan]

What happens if I'm not able to retreat every hour? Last night I put in enough bleach to raise FC to 10 ppm (~ 6 gals of 6% bleach, I think). An hour later I retested the FC and it was still at 0.5 - 1 (pump running the entire time) so I put in more bleach then had to go to bed. Working during the week I won't be about to re-treat every hour for hours at a time so are my 2 doses an evening helping or just making things worse?

 

[Bama Rambler]

When converting ammonia nothing really bad happens if you don't keep at it. It's not like algae, that starts back growing as soon as the level drops, it just takes longer to get it all oxidized but the end result is the same. Do it as often as you can. We all understand the need to have a real life to go along with the pool life.