where my chlorine gone?

[dudeeg]

Hi,

I have a simple vinyl pool in my garden. It is an oval type, holding 30.000 liters or 8000 gallons of water. I'm regularly measuring the chlorine/pH values, and keeping it on ~1mg/L and 7.2. Unfortunately we don't have here (Hungary, Europe) very good test kits like the Taylor K-2005, just the Taylor K-1000, plus I bought the R0003 reagent to be able to measure the combined chlorine. So unfortunately I don't have data like TA or CYA.
The latter is surely in the water (maybe way too much), because the pool is treated with chlorine tablets, and it is shocked with dichlor granulate (I know it is not the best idea).
Yesterday I measured a 0.5mg/L of combined chlorine so I decided to raise the chlorine level. I added ~400mg of dichlor (56% chlorine content), which is equivalent of ~7mg/L FC in my pool. I know the well known breakpoint curve of ammonia/combined chlorine.
After adding the chlorine, the pump was on for several hours. I made 4 measurements altogether, with the following results:
- before treatment: 0.5FC, 0.5CC
- 1 hour after treatment: 2.5FC, ~4CC (went up pretty much)
- 10 hours after the treatment (following morning): 0.5FC, 0.5CC
- 24 hours after the treatment (now): 0.5FC, 0.5CC

the solar cover was not on the pool during this period.

I am not sure where I am now, because practically the results showing the same concentrations as before.
Did I reach the phase II on this curve, or where am I?
https://upload.wikimedia.org/wikipe...ramination_breakpoint_curve_(theoretical).jpg

Should I add chlorine again? I'm a bit confused seeing these values.
One more: the water looked very clear before, now it is crystal clear, so no problem with that.

Thanks in advance!

 

[domct203]

There is really only two major sources of chlorine demand, UV rays (sunlight) and oxidizing organics.

I'm not sure of the "well known breakpoint curve of ammonia/combined chlorine", but I do know that you should never let your FC drop below 7.5% of your CYA level.

You should now dose the pool with liquid chlorine, aka bleach. It can be bought in different concentrations, 8.25% (common laundry bleach in the USA), 10%, 12.5% etc but they are all sodium hypochlorite, and add nothing but chlorine and a trace amount of salt.

Unfortunately without a CYA level it's impossible to know how much free chlorine you need to maintain.

 

[Mr Bruce]

If you have no way of testing CYA, it might be worth it to dump the water, refill, add a known amount of CYA (using granular, liquid or di-chlor via Pool Math) and only dose with bleach/liquid chlorine after that.

Is that an option?

 

[dudeeg]

Yes, the CYA level is completely unknown in the pool stores here. I am really wondering how could that be. I managed to have a conversation with a chemical engineer dealing with water topics. She know a lot about cyanuric acid, but she agreed that only the professionals of large pools are knowing this topic, the small garden pool owners have no clue about it, like I said even the pool shop guys don't know it.

Sure, we have normal household bleach here, but I stil have to look for it, because what I could find has only 1.5% chlorine content, which is way too low.

but I am still not sure how the chloramines remained in the water after the shock treatment. They supposed to break down.

- - - Updated - - -

If you have no way of testing CYA, it might be worth it to dump the water, refill, add a known amount of CYA (using granular, liquid or di-chlor via Pool Math) and only dose with bleach/liquid chlorine after that.

Is that an option?

I would like to avoid that. The water here is pretty expensive, and like I said: besides the measured 0.5mg/l combined chlorine I have no issue with the water at all. Doesn't smell and looks good. It is just that 0.5mg I wanted to be 0mg

 

[Mr Bruce]

FC + organics = CC. So if you increase your FC and there are organics waiting to be turned into CC, there you go.

I feel for you, 1.5% bleach is tough. At least you have a tiny pool

 

[dudeeg]

Yesterday I added 7mg free chlorine again to see what happens. After 1 hour the FC went up to 2mg/l and the CC to 4mg/l again.
Today morning the chemicals settled on 1mg free and ~0mg combined, so I'm hoping that any additional chlorine will stay as free from now on, at least for a while.

I am trying to get bleach with higher (at least 4-5%) concentration to avoid adding CYA when shocking, but most of the pool guys here are just using the convenient pool store chemicals (di/trichlor) because they are saying you cannot be sure what kind of contaminants might be in the household bleach that you would not like to see in your water.

 

[domct203]

Yesterday I added 7mg free chlorine again to see what happens. After 1 hour the FC went up to 2mg/l and the CC to 4mg/l again.
Today morning the chemicals settled on 1mg free and ~0mg combined, so I'm hoping that any additional chlorine will stay as free from now on, at least for a while.

I am trying to get bleach with higher (at least 4-5%) concentration to avoid adding CYA when shocking, but most of the pool guys here are just using the convenient pool store chemicals (di/trichlor) because they are saying you cannot be sure what kind of contaminants might be in the household bleach that you would not like to see in your water.

If you are buying a good quality bleach it should contain sodium hypochlorite, & less than 0.2% sodium hydroxide, that's it. Don't use scented or splashless types as those do contain additional additives.

https://depts.washington.edu/flowlab/Cell Analysis Facility/MSDS/Bleach_MSDS.pdf

You can look this up yourself by searching for your product's SDS (or MSDS).

 

[dudeeg]

If you are buying a good quality bleach it should contain sodium hypochlorite, & less than 0.2% sodium hydroxide, that's it. Don't use scented or splashless types as those do contain additional additives.

https://depts.washington.edu/flowlab/Cell Analysis Facility/MSDS/Bleach_MSDS.pdf

You can look this up yourself by searching for your product's SDS (or MSDS).

Thanks! Such safety data sheets are also available here for the bleach products, and we have pure -w/o additives- bleach as well. Nevertheless, some people are still afraid to use such products because they say there might be some traces of contaminants from production that are not listed on the data sheet. But if the manufacturer added a sticker "For pool use", they would accept the same product immediately

Meanwhile I've checked, the maximum chlorine concentration for domestic use here is 4.5%. Not so much. If you want to buy in higher concentration, you need permissions, and the smallest container is 25 liters/8 gals.

 

[Mr Bruce]

Using pool math, it would take 1/2 gallon of 4.5% bleach to raise FC by 3ppm in a 8k gallon pool, a "normal" day's loss. That seems very reasonable to me.

You are asking for trouble raising CYA any more going forward. Pool School - Chlorine / CYA Chart

 

[Vickery]

When you compare quality laundry bleach with a decent concentration (8.25% or more) with the same product labeled "For Pool Use" the difference is the cost of the sticker.