Thinking about Active Chlorine

[TreeFiter]

So if I understand it correctly, the concept of Active Chlorine refers to the portion of FC that is actively sanitizing. So when we take a measurement of FC, we get a number, part of which is tied up with CYA, and not actively killing algae and pathogens. The remaining portion is the Active Chlorine. The amount of Active Chlorine is dependent on the FC level and CYA.

I've been thinking about this concept, and I'm curious if there is a noticeable difference in waters with higher Active Chlorine levels and lower Active Chlorine levels. Would there be a stronger chlorine odor with higher Active Chlorine? Will this water create the characteristics typically associated with "High Chlorine"?

 

[RobbieH]

Typically, chlorine smell only occurs in a pool where CCs are present.

What are the characteristics of high chlorine?

 

[jblizzle]

The higher the active chlorine level, the more damage to skin, hair, suits, etc. If I am in a public pool after getting out my skin often feels very dry and hair is frizzy. This in not observed as much in my own pool.

Also, for a frequent swimmer, a swim suit may only last a few months in a public indoor unstabilized pool, but could last years if the water was maintained by our recommendations.

Did you see my other posts about this table today which raise this question?
https://www.troublefreepool.com/~richardfalk/pool/HOCl.htm

 

[TreeFiter]

Typically, chlorine smell only occurs in a pool where CCs are present.

What are the characteristics of high chlorine?

The characteristics I had in mind were along the lines of what Jbizzle hit on. The bleaching power, and the things people usually blame on high chlorine, even though it isn't always chlorine related.

As for smell, Chloramines are usually responsible for the chlorine odor under normal circumstances, but when you add a lot of chlorine to a pool, you will smell it. For that matter, take a whif of liquid chlorine. There is no doubt that there is a smell.

I'm not necessarily referring to normal situations, but thinking along the lines of a hypothetical experiment. Maybe an example where there are two identical pools, but one has FC=30, but CYA=90 and the other with FC=30 and CYA =20. The same FC, but with different CYA levels, the Active Chlorine levels would be very different.

 

[RobbieH]

I should have said chlorine smell in a properly balanced pool will be from CCs. Even at SLAM level, I don't smell chlorine in my pool.

I realize the bottle smells, but I hope nobody is keeping their pool at 8.25%.

 

[TreeFiter]

The higher the active chlorine level, the more damage to skin, hair, suits, etc. If I am in a public pool after getting out my skin often feels very dry and hair is frizzy. This in not observed as much in my own pool.

Also, for a frequent swimmer, a swim suit may only last a few months in a public indoor unstabilized pool, but could last years if the water was maintained by our recommendations.

Did you see my other posts about this table today which raise this question?
https://www.troublefreepool.com/~richardfalk/pool/HOCl.htm

What you describe is along the lines of what I was hoping for. I have been thinking about using this concept as a teaching/training tool.

Maybe mix up two batches of water in buckets, both with the same FC, but different CYA levels. Then have students guess which has "high chlorine".

Possibly take it a step farther to add a little bit more shock value, where a lower FC level (maybe 8ppm) with very low CYA (maybe 0ppm) would appear to have "high chlorine" while the other sample with higher FC (maybe 20ppm) and much higher CYA (maybe 100ppm) would appear to be OK.

Then you could test the FC in each and see that the bucket with the lower FC level appears to have "high chlorine".


As for the table, I've seen that in the past. In this case I'm more concerned with the types of things the average person could pick up on, like odor, itchy dry skin, frizzy hair, etc. However, I came up with a question when I looked at it. Why do we see less than 50ppm Active Chlorine when FC is at 100ppm? Where does the other half go?

 

[TreeFiter]

I should have said chlorine smell in a properly balanced pool will be from CCs. Even at SLAM level, I don't smell chlorine in my pool.

I realize the bottle smells, but I hope nobody is keeping their pool at 8.25%.

I agree, you shouldn't typically be able to smell it. I have however, been in situations where due to the nature of a weekly maintenance schedule, it was necessary to bring FC way up, knowing it was going to fall back down quickly (usually in a swamp situation). At those higher levels, the smell becomes pretty obvious. But again, these aren't normal circumstances, and I certainly don't recommend doing this on a regular basis.

 

[JasonLion]

Chlorine actually has three forms (that we care about in pools): hypochlorous acid (HOCl), hypochlorite ion (OCl−), and bound to CYA. Only the hypochlorous acid is "active" chlorine.

 

[woodyp]

I should have said chlorine smell in a properly balanced pool will be from CCs. Even at SLAM level, I don't smell chlorine in my pool.

I realize the bottle smells, but I hope nobody is keeping their pool at 8.25%.

Welllllllll.......even at 50 or 60 cya my pool loses 4 ppm daily in the Texas heat. So I take it to 8 to KEEP 4 ppm minimum in at all times.

I take it back to 8 before a party too.

 

[chem geek]

The hypochlorous acid is a faster disinfecting agent than hypochlorite ion by at least a factor of 20 because cells have negatively charged surfaces so tend to repel negatively charge hypochlorite ion, but for oxidizing power hypochlorite ion is sometimes the active agent. It depends on the molecule getting oxidized. Some get substitution or oxidation reactions from hypochlorous acid and others by hypochlorite ion and others by both. Usually the pH dependence gives away which is the oxidizing agent.

As for smell, hypochlorous acid does outgas from the pool (and does so more than chlorine gas itself at normal pool pH) so at higher active chlorine levels you can faintly smell it especially if you churn up the water to increase aeration. This is most noticeable in spas due to the higher water temperature which not only increases the rate of outgassing directly but also increases the active chlorine level at the same FC/CYA ratio (more hypochlorous acid is unbound from CYA at hotter temperatures). It's true that the chloramines are more volatile so smell more than chlorine, but chlorine does faintly smell.

 

[bridgman]

I do get a faint "bleach smell" when opening the cover of my hot tub (at, say, FC=5, CYA = 30-ish and CC=0-ish), but it's a lot weaker than the smell in the laundry room after using bleach in the washing machine.

And no, I don't normally use pool chlorine in the washer, just that one time and I diluted it 50/50 before pouring it in

 

[chem geek]

Just FYI, the recommended levels of bleach to be used in washing machines is 1/2 cup per load and a washing machine load uses 23 gallons for a standard machine (15 gallons for ENERGY STAR certified), but that's multiple fill/drain only one of which would use the chlorine bleach. So let's conservatively use half so 12 gallons where 1/2 cup of 6% bleach would be 161 ppm FC (with the newer more concentrated 8.25% bleach it would be 221 ppm FC). Though there is no CYA in the water, the pH rises significantly to close to 8.6 so the hypochlorous acid concentration is equivalent to around 21 ppm FC at pH 7.5.

 

[TreeFiter]

Just FYI, the recommended levels of bleach to be used in washing machines is 1/2 cup per load and a washing machine load uses 23 gallons for a standard machine (15 gallons for ENERGY STAR certified), but that's multiple fill/drain only one of which would use the chlorine bleach. So let's conservatively use half so 12 gallons where 1/2 cup of 6% bleach would be 161 ppm FC (with the newer more concentrated 8.25% bleach it would be 221 ppm FC). Though there is no CYA in the water, the pH rises significantly to close to 8.6 so the hypochlorous acid concentration is equivalent to around 21 ppm FC at pH 7.5.

Does this make the assumption of no CYA present (as would be expected in a washing machine)? 21ppm with no CYA is screaming high. Thanks for this chem geek. It really paints a good picture of how far apart pool water and washing machine concentrations are.

 

[JamesW]

Does this make the assumption of no CYA present (as would be expected in a washing machine)? 21ppm with no CYA is screaming high.

Yes, that is a very high chlorine concentration. However, the other factor is the total contact time, which in a washer will be fairly brief.

Therefore, the higher values are needed to work in the short amount of time the chlorine has to work. How much is actually needed depends on what you're trying to achieve, such as disinfection etc.

 

[Patrick_B]

There is barely a detectable odor of Chlorine from a freshly opened Bleach container IMO. You can hardly smell it.

 

[TreeFiter]

There is barely a detectable odor of Chlorine from a freshly opened Bleach container IMO. You can hardly smell it.

I suppose its the kind of thing that would depend on a person's sensitivity to the odor.

 

[bridgman]

The smell in the laundry room is much stronger after washing with bleach is much stronger than the smell of a freshly opened bottle of bleach. I'm trying to resist the urge to capture the drain water from the washing machine and test the CC level.

The bleach smell in the hot tub is less than the smell from a bleach bottle, although not *that* much less because the water is warm and there's a lot of surface area that is covered up most of the time and the smell gets saved up until you remove the cover

 

[JasonLion]

In a spa, unlike a pool, CC is fairly common. Even if the CC level in the water has gone down to zero, volatile CC that has outgassed can still be trapped under the cover to amuse entertain surprise you when you open the cover.

 

[TreeFiter]

The smell in the laundry room is much stronger after washing with bleach is much stronger than the smell of a freshly opened bottle of bleach. I'm trying to resist the urge to capture the drain water from the washing machine and test the CC level.

The bleach smell in the hot tub is less than the smell from a bleach bottle, although not *that* much less because the water is warm and there's a lot of surface area that is covered up most of the time and the smell gets saved up until you remove the cover

This is something I hadn't really thought about. The Chlorine used in laundry is there to do a job. By doing that job, a portion of it might be converted to CCs. I would be curious as well about the final CC levels in a load of laundry.

Does anybody care to refresh my memory on what specifically causes FC to convert to CCs? Isn't it related to the way it reacts with undesireables in the water?

I think I also made the assumption that by adding significant amounts of chlorine while shocking a pool, I would only be dealing with FC, but if I'm shocking the pool, there is going to be plenty of stuff in the water for that FC to start working on. I could be smelling CCs being generated rapidly from the newly introduced FC.

 

[Patrick_B]

If you decide to do that, you will need to order a refill of FC reagents pretty soon. :lol: