slow and steady chlorination idea- first tests

[Patapsco Mike]

I stumbled upon a pretty easy way to continuously chlorinate for up to a week very simply. My recent purchase of a Liquidator got me to thinking. If chlorine sinks, then you could submerge something right in the pool, from which chlorine would continuously enter the pool. Looking at a 96 oz jug of 6% Chlorox, I thought "why not?" I just took the cap off the chlorine bottle and chucked it in my pool. I guided it down to the bottom with my leaf net so that it landed upright. I put one in the deep area, and one in the shallow area. At two days, both were still about 2/3 full of chlorine. After a week, they had about an inch of chlorine still in the bottom. After 10 days, it was pretty much emptied of chlorine, with maybe just a tiny bit left when I dumped them out.

So- my theory is- if you know how many jugs of chlorine your pool needs every 10 days, you can just submerge that many bottles (upright) in the bottom of your pool and they will slowly, evenly, and continually release that chlorine into your pool over that time... I use about 3 bottles every 10 days, and putting three upright on the bottom of my pool kept my chlorine levels constant for almost two weeks with zero effort. I'm pretty excited about it, and thought I'd share. I'm looking forward to seeing how long the big Chlorox bottles last.

I think it works because the relatively narrow opening in the top of the chlorine jug allows for a slow exchange by diffusion. I suspect you could slow it even more by only opening the foil at the top of the chlorine jug by 1/2. You could speed it up by putting the jug in an area with more flow.

I still need to play around with this to really dial it in, so use the above as a starting point if you want to try this.

I've been lurking here most of the summer. Really enjoy the site.

 

[The Mermaid Queen]

Welcome to TFP!

Last year, someone on PF posted their 'vacation method' of chlorination... they poked a small hole (holes?) in the bottom and cap of several bleach jugs and strung them across the pool. The heaviness of the bleach allowed it to seep out over the vacation time, and they returned to a clean pool.

My only concern with your method of putting the open jug onto the bottom of the pool is that the jug would fall over and dump the bleach out quickly, bleaching out the liner...

 

[Belldiver]

You could just fill the bottom of the jug with some rocks to weight it down. You might want to jump in with it to make sure it sits down right though. Interesting idea...

 

[ktdave]

Very cool idea! I agree stringing them across the pool, maybe a foot under the surface, would be better (more distance from liner), but kudos on the ingenuity.

 

[Patapsco Mike]

Here's the thing though- it's not coming out of the bottle full strength- it's pre-diluted. It works just like the Liquidator does, just on a smaller scale. The full strength chlorine sits in the bottom of the jug. It slowly dilutes into the water above it in the jug, presumably forming a cline. Like a thermocline, but with chlorine- a chlorocline. At the very surface of the chlorine jug, the pool water interacts with the more chlorinated water layer, further diffusing the solution.

I think this would come out at a very consistent and even rate from the time you put the jug in until the time it's fully emptied of chlorine. This is because that interface will stay pretty much the same the whole time. With holes in a bottle, the chlorine is going to drain out really quickly until it reaches the level of the lowest hole, then it will come out very very slowly.

And no weight is necessary because the chlorine is considerably heavier than the pool water. It sinks much faster and more easily than you might think.

 

[The Mermaid Queen]

Ok, this might be a DUH question, but since the Cl is heavy (at least heavier than the water) how can it come out of the TOP of the jug?

I don't know what a cline is, so perhaps that is why I can't figure this out??

 

[JasonLion]

There are two possible processes, flow and diffusion. Flow is just like water flowing around. Diffusion is essentially mixing at the molecular level. When you pour bleach into a pool the bleach flows around in the water and spreads out quite a bit while still remaining seperate from the water for a little while. At the same time bleach near the bleach-water interface starts to mix with the water in a process called diffusion. The rate of diffusion is proportional to the surface area of the bleach-water interface (and the difference in concentration, but that is secondary in this case). When you are pouring bleach into the pool and it is flowing around well (because you added it to the skimmer or near a return) that interface becomes quite large, so the process goes quickly. With a bleach jug, with only a narrow openning at the top, diffusion goes quite slowly.

 

[ktdave]

A "cline" is a layered body of "something" that exists within another body. In this case, I guess we have a density -cline (maybe more technically a pycnocline) where the more dense chlorine falls below the lesser dense water.

Don't know if this helps with explanation (or even if it is absloutely correct), but I gave it a try.

As far as the science of how it gets out of the top of the jug, probably diffusion, where something at a greater concentration tends to spread out to be less concentrated

 

[The Mermaid Queen]

Cool, thanks for making this relatively understandable!!

However, if it is simply diffusion, (which I did not think of) then the principle of the liquidator would be shot down, since you layer water over the bleach. If the bleach diffused into the pool water, would not the bleach in the liquidator simply diffuse upward, making the entire container full of less concentrated bleach, and not the layers??

(I really think this is a neat idea, I am just trying to understand it!) (sometimes it just does not pay to ask "Why?" )

 

[MeSue]

Just taking a stab in the dark here, but isn't the Liquidator an enclosed container with relative little flow going through it? (I have no idea--only seen it in pictures.) Contrast that to the open bleach jug which will have water flowing around it all the time the filter pump is running. My guess is that the flow of water aids the diffusion process.

Guys, jump in and correct if I am off-base here...

 

[JasonLion]

Diffusion is why the Liquidator works at all. Bleach diffuses out of the bleach layer and into the pool water layer, thus chlorinating the pool. The layers don't mix because the salts don't diffuse into the pool water significantly. That is why the Liquidator ends up with a bunch of salt in the bottom that needs to be cleaned out occasionally.

However, even without that they wouldn't mix all that quickly. Chlorine diffusion is really slow unless there is a large surface area to work over. Both the Liquidator and the bleach jug limit the surface area to keep the bleach from getting into the pool too quickly. The water in the pool water layer also gets replaced slowly, so it's chlorine concentration never gets that high. Without the salts, they would eventually mix but only at about the time you ran out of bleach

In contrast, pouring bleach into a return stream spreads the bleach out so that it has a very large surface area, and thus diffuses effectively.

 

[chem geek]

What I find interesting is that the salt in the chlorine layer doesn't diffuse much, or at least not as quickly as the hypochlorous acid, into the water layer. If you have a bunch of salt at the bottom of a glass of water, it will dissolve, but I don't think it ends up with a strong gradient with denser salt water on the bottom, at least not by very much. So something about the nature of concentrated hypochlorous acid solutions interfacing with water has preferential diffusion for the chlorine vs. the salt. I wonder if it has anything to do with the fact that the hypochlorous acid is polar and not charged whereas the salt ions are charged?

It would be interesting to see if the jugs of chlorine at the bottom end up with any solid salt at the bottom, assuming they are removed before the chlorine has completely diffused. Perhaps it takes multiple cycles of new chlorine addition in The Liquidator before the salt concentration builds up enough to come out as solid so that one jug of chlorine wouldn't show that salt -- but removing it early might still show a much higher salt concentration in what remains. Taking the jug out before all the chlorine is gone would help reduce the amount of salt added to the pool water (not that it's a big deal).

Richard

 

[Patapsco Mike]

Richard- salt does form extremely strong clines called pyncnoclines. That's the principle cline that forms in saltwater embayments (e.g. Chesapeake Bay). By day, I'm a scientist (can you tell?). I suspect that what sets up in the jug is a chlorocline.

I don't know if there were any salts left in the jug- I just dumped them out at the end of the 10 days when there was very little if any chlorine left. I really didn't pay attention, but I will next time.

I tell you this, it's nice only adding chlorine every 10 days instead of every day or every other day. I'm really liking my discovery. At first, I was thinking that I should return my liquidator. But the one downside of using jugs is that if there is activity in the pool, the jugs will get knocked over. So you'd have to take them out first. As long as you don't flip them, you could just set them on the deck and put them back in after your swim. But that's a bit of a pain. So I think this jug thing is something that I would mostly do when leaving for vacation, or at the very beginning or end of the swim season when the pool isn't getting a lot of use (like now). Just one more trick to make my pool a bit more trouble free- which is the point I guess...

 

[chem geek]

Mike,

Thank you so much for that creative idea regarding the jugs of chlorine and pointing me in the direction of clines (of various types -- thank you). For those with a deep end of the pool that rarely gets disturbed, one could set up a plastic crate to fit 4 bottles, just like the one I get with my chlorinating liquid, and have anywhere from 1-4 continuous chlorine dispensers that won't tip over. This may be a very practical way for at least some pools to get some automatic chlorination with virtually no effort!

The only thing I might be concerned about is a buildup of chlorine concentration at the bottom of the pool, but with pools with floor drains I don't think that would occur. For vinyl pools without a floor drain, that might be more of an issue.

Richard

 

[kal2002]

I just found this posting from 2007. Were there any updates since then? This sounds like a great alternative to manually adding chlorine everyday. Has anyone else tried it?

 

[Beez]

I just found this posting from 2007. Were there any updates since then? This sounds like a great alternative to manually adding chlorine everyday. Has anyone else tried it?

Wow, thanks for dredging this up!

I wonder if I sunk a jug into the deep part of my spillover spa would it work like a liquidator? There is only one sure way to know! I just can't resist...

 

[kal2002]

Hi Beez, I can't wait to hear your verdict....Please keep us posted.

 

[Richard320]

This is an interesting old thread.

I see a use for it on vacation, perhaps. But I see it as impractical on a daily basis. You couldn't vacuum where the jugs are sitting. Couldn't brush. And certainly no rough-housing in the pool!

 

[kal2002]

Re:

Last year, someone on PF posted their 'vacation method' of chlorination... they poked a small hole (holes?) in the bottom and cap of several bleach jugs and strung them across the pool. The heaviness of the bleach allowed it to seep out over the vacation time, and they returned to a clean pool.

I am actually more interested in the concept of the floating bleach jugs without having to string them. I like the idea of them floating around the pool like the floaters for the chlroine tabs.

 

[Beez]

This is an interesting old thread.

I see a use for it on vacation, perhaps. But I see it as impractical on a daily basis. You couldn't vacuum where the jugs are sitting. Couldn't brush. And certainly no rough-housing in the pool!

Well, the way the OP described it would definitely be impractical on a routine basis, but I'm trying it from my spill over spa. Honestly, I don't hold out much hope for it for several reasons, it just seems like an interesting experiment with little risk involved.

I wonder if the bleach will continue to diffuse even when there is no flow around it(i.e. when the pump is off)? If so, it's going to waste a lot of bleach. At this point, the only thing I can verify is that the jugs do sink! I will be monitoring my FC level every morning for a while to see what effect it has. The worst I can see happening is that I'll waste a few jugs of Chlorox...