Clorine Addition After Exiting Spa Vs. Before Entering Spa

[Nat]

I've ben reading on the Forum that the clorine (dichlor or bleach, depending on when water was last changed) should be added right after you get out of the spa. The amount of clorine carrier to add is the amount needed to increase the free chlorine to 3.5 ppm, correct?

I was under the impression that it would be better to add the chlorine right BEFORE entering the spa, because you would then have 3.5 ppm of chlorine available to disinfect the water at the beginning of your soak.

I used to add the chlorine after exiting the spa (1.5 tsp. dichlor or 1/3 cup bleach in 330 gallons of water) and the next day I would measure (with a Taylor test kit) the free chlorinie level prior to using the spa, and it was 0 - 0.5 ppm. Basically non-existent. The instructions that came with my spa say to add the chlorine immediately before using the spa.

Why is it suggested to add the chlorine after using the spa?

Thanks.

--Nate

[TinyBubbles]

Hi Nate, I can weigh in on why I add chlorine after soaking. I do it so that I'm stewing in less harsh chemicals than I would be if I added it before. I do change this routine, however, if I have friends soaking. In this case, I add a little before and a lot after. Since chlorine should kill things in a short amount of time, there shouldn't be any harmful buggers still living in your spa the next day when the chlorine residual is practically non-existent. I, also, use an N2 cartridge.

[chem geek]

Ideally, you would have a fairly constant level of Free Chlorine in the spa at all times. Also, since the chlorine usage is greatest when you are in the spa, it would make sense to add the chlorine before you get in. However, doing so does tend to expose you to more chlorine and that can smell in the short run as it combines with your sweat (ammonia-like compounds) to produce monochloramine which takes a short time to break down, but is volatile. So to reduce the chlorine smell, the procedure of adding chlorine afterwards is what most people follow. As long as there is at least some residual, say 1 ppm FC, when you get in, then you are assured that there are minimal pathogens in the water. It is true that the kill time for newly introduced pathogens would be slower, especially if the chlorine got used up while in the tub, so the advice of adding some more when sharing the tub makes sense.

It's really a personal choice. For extra sanitation, you can add it before you get in, but if you find too much of a chlorine smell then you can change your routine to add some before and some after or to just add it after. Regardless of when you add it, keeping the cover off for 10 minutes or so before you get in (and after you've added chlorine if you are adding it before) helps to reduce the smell that builds up under the cover.

In your specific situation, it sounds like you need to add a little more chlorine if you are adding it when you get out since it isn't lasting long enough. If you measure around 1 ppm FC the next day, then you're probably in pretty good shape. This assumes, of course, that the CYA level isn't too high. I've said that 4 ppm FC at 20 ppm CYA is a conservative level to shoot for but this depends on when you add the chlorine, how often, and how quickly it gets used up since you never want the FC to get to zero.

Richard

[David66]

My compromise is to add the chlorine each morning. I add it first thing after waking up, then leave the cover open and run the jets while I get ready for work, then shut it down and close the cover just before leaving for work (usually 20 minutes or so later). My usual dose is now 3 oz. of bleach. When I go to soak in the evenings, it hasn't been a full 24 hours since adding chlorine, more like 12 or so. This seems to allow some decent ppm readings for when I enter, without being so high that I smell a lot of chlorine. I add chlorine in the morning daily whether I use the tub or not (or try to...sometimes doesn't get done if I'm outta town or something). THEN, I also add some after a soak to kill anything I've introduced. I don't worry about it getting too high when I add some the next morning, because rarely do I use it two nights in a row, but even if I did I think it would be at a safe level by the time I used it some 10 to 12 hours later.

AND, if I know that I have a large group coming over, I'll try to add some a few hours before they visit in anticipation just to be on the safe side. This might not be a full does because I try not to get it to the point where you can smell the chlorine too much, and I try to add it a few hours before they show up if possible. And definitely a healthy dose after they leave.

By the way, I'm still feeling my way through chlorine dose volumes for these additions. I'm only on my second fill of water and my first one got all screwed up with a CYA level that was too high making it almost impossible to maintain any ppm of FC at all for any period of time.

David

Ideally, you would have a fairly constant level of Free Chlorine in the spa at all times. Also, since the chlorine usage is greatest when you are in the spa, it would make sense to add the chlorine before you get in. However, doing so does tend to expose you to more chlorine and that can smell in the short run as it combines with your sweat (ammonia-like compounds) to produce monochloramine which takes a short time to break down, but is volatile. So to reduce the chlorine smell, the procedure of adding chlorine afterwards is what most people follow. As long as there is at least some residual, say 1 ppm FC, when you get in, then you are assured that there are minimal pathogens in the water. It is true that the kill time for newly introduced pathogens would be slower, especially if the chlorine got used up while in the tub, so the advice of adding some more when sharing the tub makes sense.

It's really a personal choice. For extra sanitation, you can add it before you get in, but if you find too much of a chlorine smell then you can change your routine to add some before and some after or to just add it after. Regardless of when you add it, keeping the cover off for 10 minutes or so before you get in (and after you've added chlorine if you are adding it before) helps to reduce the smell that builds up under the cover.

In your specific situation, it sounds like you need to add a little more chlorine if you are adding it when you get out since it isn't lasting long enough. If you measure around 1 ppm FC the next day, then you're probably in pretty good shape. This assumes, of course, that the CYA level isn't too high. I've said that 4 ppm FC at 20 ppm CYA is a conservative level to shoot for but this depends on when you add the chlorine, how often, and how quickly it gets used up since you never want the FC to get to zero.

Richard

[chem geek]

I'm only on my second fill of water and my first one got all screwed up with a CYA level that was too high making it almost impossible to maintain any ppm of FC at all for any period of time.

David,

It sounds like you've got a good plan. It is very strange that high CYA levels would lead to apparently greater chlorine usage as higher CYA levels make chlorine less reactive so usually you would find somewhat less chlorine usage (from oxidizing organics -- though combining with ammonia still happens very quickly). The only time this wouldn't happen would be if something were growing in your tub and not getting killed off fast enough such as algae. This is very typical in pools where high chlorine usage with high CYA levels often means an impending algae bloom, but in spas/tubs this is far less common (though still possible).

Richard

[David66]

I'm only on my second fill of water and my first one got all screwed up with a CYA level that was too high making it almost impossible to maintain any ppm of FC at all for any period of time.

David,

It sounds like you've got a good plan. It is very strange that high CYA levels would lead to apparently greater chlorine usage as higher CYA levels make chlorine less reactive so usually you would find somewhat less chlorine usage (from oxidizing organics -- though combining with ammonia still happens very quickly). The only time this wouldn't happen would be if something were growing in your tub and not getting killed off fast enough such as algae. This is very typical in pools where high chlorine usage with high CYA levels often means an impending algae bloom, but in spas/tubs this is far less common (though still possible).

Richard

Richard,

Well, I think the plan of adding bleach in the morning does make a bit of sense.

Now I'm confused on why it seems that my FC levels don't last very long. Remember, I'm a newbie at this hot tub thing, but I think I'm fairly smart and a quick study. From reading your posts in the forum, and from your advocation of using bleach vs dichlor, isn't it because you don't want high CYA levels? And you don't want high CYA levels because it causes chlorine to become less effective? Is becoming less effective the same as lasting as long as it should?

If "less effective" is different than "not lasting very long", what factors lead to chlorine being "used up" faster than desired? How can I prevent that?

In other words, my CYA is at least somewhat on the low end. So, that means that 4ppm chlorine will be more effective at killing nasty bacteria than if my CYA levels were high and my chlorine was 4ppm. But does it also extend to HOW LONG a decent level of FC exists? For example, if I started out at 10 ppm FC with a high CYA, and 20 hours later it was down to 0 ppm FC, then at a low CYA, I would have 3 ppm 20 hours later instead of 0? These are hypothetical numbers, I'm just trying to get at the overall concept.

Or, are you saying that the CYA has nothing to do with how fast your tub falls from 10 ppm to 0 ppm. What I want to know is this: what can I do to maintain the FC for the longest possible amount of time? Is there an optimum water chemstry when it comes to CYA, pH, Alk, Hardness, etc.? Because I'll definitely do my best to get it there. I just don't know what it is.

By the way, my tub also suffers from a really screwed up pH/Alk levels, both way too high, which I'm trying to correct. Maybe that is contributing to how long my FC is lasting?

On a separate note, I'm really amazed at how much work the hot tub thing is. I can't imagine adding chlorine 2 or 3 times a day just to "maintain" 1 to 3 ppm FC. But that's what I'd have to do with the water chemistry I've had in the first 3 months of spa ownership. Even now, after a water change, my FC drops from 10ppm down to zero in less than 12 hours. I added 3 ounces of bleach (Clorox, regular, unscented, 375 gal. tub) at 7am this morning, and when I tested it at 6pm tonight, it reads zero. What on earth do I have to do to maintain at least 1 ppm chlorine for a 24 hour period? Add the whole damn jug? Given that I have ozone (and the D1 ozone system is supposedly very good) and the Vision cartridge, I don't need high levels of chlorine at all times. I believe if I could maintain between around 2 or 3, I'd be safe. But I get it dropping to zero all the time.

My pool is 1/30th the work. Literally. No changing the water every 3 months. No daily testing (sometimes multiple times per day). No daily addition of chlorine. No monthly washing of filters. No day-long balancing of pH/ALK sessions. No weekly addition of Defender this and Enzyme that. No anti-foam agent. No washing of the fiberglass surfaces when changing the water and "spa gloss" or whatever is need to protect the surface. No worrying about chlorine's adverse effects on a $500 cover. No worrying about what happens to the $10,000 spa when the electricity goes out. No "leave the cover open, then remember to go out and close the cover 30 minutes later". Jeeez! Enough already. I'm to the point now where it's hard to fit in soaking among all the additions, tweaking, balancing. I'm lucky if I use the thing twice a week. "Oh, I'd like to soak tonight, but I just did my weekly addition of Defender, Enzyme and Spa Shock...better to wait 'til tomorrow".

Somebody help me get a handle on this water thing so it becomes easy and not such a chore! If I ever have a problem with the tub mechanically, I think my dealer will be great to take care of it, but they are pretty much clueless on the water chemistry thing. Their advice: add a capful of dichlor after each soak, Defender once a week and otherwise don't worry about it. THAT, my friend, is NOT the way to go. Using their advice for the first month, I had all kinds of water problems...the worst being a yellow gunky crap. Not to mention CYA levels through the roof after about 2 months of dichlor, and crazy amounts of foaming.

I'm about ready to list this sucker in the paper and rent a motel room that comes with a hot tub whenever I need a hot tub fix!

Then I remember that it's really cool to have and just outside my door.

David

[tony]

On a separate note, I'm really amazed at how much work the hot tub thing is. I can't imagine adding chlorine 2 or 3 times a day just to "maintain" 1 to 3 ppm FC. But that's what I'd have to do with the water chemistry I've had in the first 3 months of spa ownership. Even now, after a water change, my FC drops from 10ppm down to zero in less than 12 hours. I added 3 ounces of bleach (Clorox, regular, unscented, 375 gal. tub) at 7am this morning, and when I tested it at 6pm tonight, it reads zero. What on earth do I have to do to maintain at least 1 ppm chlorine for a 24 hour period? Add the whole damn jug? Given that I have ozone (and the D1 ozone system is supposedly very good) and the Vision cartridge, I don't need high levels of chlorine at all times. I believe if I could maintain between around 2 or 3, I'd be safe. But I get it dropping to zero all the time.

My pool is 1/30th the work. Literally. No changing the water every 3 months. No daily testing (sometimes multiple times per day). No daily addition of chlorine. No monthly washing of filters. No day-long balancing of pH/ALK sessions. No weekly addition of Defender this and Enzyme that. No anti-foam agent. No washing of the fiberglass surfaces when changing the water and "spa gloss" or whatever is need to protect the surface. No worrying about chlorine's adverse effects on a $500 cover. No worrying about what happens to the $10,000 spa when the electricity goes out. No "leave the cover open, then remember to go out and close the cover 30 minutes later". Jeeez! Enough already. I'm to the point now where it's hard to fit in soaking among all the additions, tweaking, balancing. I'm lucky if I use the thing twice a week. "Oh, I'd like to soak tonight, but I just did my weekly addition of Defender, Enzyme and Spa Shock...better to wait 'til tomorrow".

Somebody help me get a handle on this water thing so it becomes easy and not such a chore! If I ever have a problem with the tub mechanically, I think my dealer will be great to take care of it, but they are pretty much clueless on the water chemistry thing. Their advice: add a capful of dichlor after each soak, Defender once a week and otherwise don't worry about it. THAT, my friend, is NOT the way to go. Using their advice for the first month, I had all kinds of water problems...the worst being a yellow gunky crap. Not to mention CYA levels through the roof after about 2 months of dichlor, and crazy amounts of foaming.

I'm about ready to list this sucker in the paper and rent a motel room that comes with a hot tub whenever I need a hot tub fix!

Then I remember that it's really cool to have and just outside my door.

David

Though I agree a pool is a lot easier to maintain, your spa shouldn't be too difficult. I generally spend about fifteen minutes once a week testing and adding chems with a Taylor kit. The chlorine thing is very easy...just add enough chlorine to reach 4 ppm after use, leave the cover open with the jets going for a few minutes, then close until you use it again. If you go more than a couple of days of non use, dose again. Shock when needed. Though ideally you like to maintain a level of free chlorine, it is not practical...just let it drop. Add chlorine before use if you feel more comfortable but I prefer to soak in practically chlorine free water. It really does get easier. BTW, you don't have to wait to use your spa after adding Defender or Enzyme and if you shock with non chlorine shock...you can use the spa after about twenty minutes. Besides...after owning your own tub, you'll probably never want to use a public one.

[David66]

Though I agree a pool is a lot easier to maintain, your spa shouldn't be too difficult. I generally spend about fifteen minutes once a week testing and adding chems with a Taylor kit. The chlorine thing is very easy...just add enough chlorine to reach 4 ppm after use, leave the cover open with the jets going for a few minutes, then close until you use it again. If you go more than a couple of days of non use, dose again. Shock when needed. Though ideally you like to maintain a level of free chlorine, it is not practical...just let it drop. Add chlorine before use if you feel more comfortable but I prefer to soak in practically chlorine free water. It really does get easier. BTW, you don't have to wait to use your spa after adding Defender or Enzyme and if you shock with non chlorine shock...you can use the spa after about twenty minutes. Besides...after owning your own tub, you'll probably never want to use a public one.

Thanks for the reply. I feel better already!

I like your approach, and it fits well with my strategy of dosing each morning. As I'm getting a handle on how much bleach it takes to reach a decent level of FC (8-10ppm), then how long it takes to drop to 1ppm it seems as though if I could add chlorine at about 3 or 4pm each day, that'd be ideal, because we normally soak between 8 and 10 pm, so by that time the levels would have dropped to be fairly low, yet allowing for at least SOME chlorine in the tub when we get in. But, that's not going to happen since I'm at work at that time 5 days out of the 7. Since I'm adding it in the morning every day, and since I have ozone and the vision cartridge...it'd be great if I could be assured that this practice would result in water that was safe when we soaked, even if there isn't any free chlorine at the actual time of soaking. (Of course, I would also add some after each soak session and a bigger dose for more people).

Maintaining a level of free chlorine is just a beast. I mean, it seems like I'd have to be adding chlorine every 6 hours or so. I guess that's the biggest surprise of hot tub ownership vs a pool. With a pool, you get an idea of how many pellets to have in the pool to maintain the desired ppm of free chlorine, and then it's a cinch.

I think somebody should invent a unit that could do this automatically. Load it up with a half gallon of bleach and let it add some every 8 hours or something like that.

One question: you mention "shock when needed". How does one determine when it is needed? Or should I just do it weekly? My dealer gave me a bottle of Pro Team Spa Shock. I assume it is non-chlorine shock. Would it be wise to use that one week, and then maybe shock with chlorine every other week?

Thanks,

David

[chem geek]

You mentioned you had an ozonator. This could be part of the problem of higher than expected chlorine usage since ozone can actually oxidize chlorine to chlorate thereby using up chlorine faster. It's a delicate tradeoff since an ozonator is also supposed to oxidize organics and if it did this efficiently then chlorine wouldn't have to and chlorine usage would be lessened. It does seem to me from the posts on this forum that most ozonators end up causing chlorine usage to increase rather than decrease. So if it is possible for you to turn off your ozonator, you might try that and see if it makes a difference in your chlorine usage. I suspect that at higher CYA levels, the disinfecting chlorine level was lower so it took longer for the ozonator to break it down. Now that you have a lower CYA level and higher disinfecting chlorine level (so that pathogens are killed more quickly), the ozonator is breaking down the chlorine faster.

As for the CYA vs. chlorine, high CYA makes the same Free Chlorine (FC) level less effective so kills pathogens more slowly and breaks down ammonia and organics more slowly. However, chlorine still combines with ammonia very quickly even at high CYA levels so the typical scenario with high CYA is that chlorine usage is still high though perhaps a little lower than at lower CYA, but that Combined Chlorine (CC) shows up (and this is mostly monochloramine which is chlorine combined with ammonia and has not been fully broken down). At the lower CYA levels, you don't measure CC as often (because the chlorine fully breaks down ammonia more quickly) and pathogens are killed more quickly.

Typical chlorine usage is around 3-4 ppm FC per day for one bather in a hot tub every day in 350 gallons. That seems to be typical of what is seen on this forum where most add enough chlorine to get to around 4 ppm FC and then have a little chlorine remaining when they next get in.

As for automatic chlorine feeders, there are peristaltic pumps available and there is The Liquidator talked about here, but it was designed for pool volumes so I don't know if it would work for a spa -- it would certainly have to be dialed down for fairly low dosing. The main reason that a hot tub is more work than a pool (usually) is that it is such a small volume of water so small changes have larger effects. Also, the bather load is much higher (bathers per water volume) so a hot tub becomes more like a commercial pool with many bathers and that is also more difficult to manage.

In theory, with an ozonator, you shouldn't have to shock at all as the ozonator should be oxidizing organics. Even without an ozonator, if you maintain chlorine levels and keep the cover off for a while after adding chlorine then you shouldn't need to shock very often. Generally, if you don't measure any Combined Chlorine (< 0.5 ppm is OK) then you don't need to shock, though it won't hurt.

By the way, you talk about the ease of maintenance for your pool, but unless you have a saltwater chlorine generator (SWG), then your automatic chlorine feeder is most likely a Trichlor feeder and that is increasing the CYA level in your pool. If you don't use an alagecide (e.g. PolyQuat 60) or a phosphate remover, then you risk getting algae as the CYA level climbs. For every 10 ppm FC added by Trichlor, it also adds 6 ppm to CYA. If instead your feeder is a Cal-Hypo feeder, then this won't increase the CYA level but it will increase Calcium Hardness (CH). For every 10 ppm FC added by Cal-Hypo, it also adds 7 ppm to CH. People who use bleach or chlorinating liquid for their pool add it every day or two unless they have an automatic doser such as The Liquidator I referred to above or unless they have an opaque pool cover (like I have) in which case they add chlorine twice a week.

Richard

[tony]

One question: you mention "shock when needed". How does one determine when it is needed? Or should I just do it weekly? My dealer gave me a bottle of Pro Team Spa Shock. I assume it is non-chlorine shock. Would it be wise to use that one week, and then maybe shock with chlorine every other week?

I shock with non chlorine shock once per week and never accumulate combined chlorine. I have tried all different ways and like this best. Non chlorine shock seems to be better at preventing CC while shocking with chlorine is better at eliminating existing CC. Pro Team Non Chlorine Spa Shock seems to be a buffered MPS. You could use this weekly and shock with chlorine only when you register any CC (total chlorine - free chlorine = combined chlorine) or you could alternate every other week with chlorine and non chlorine shocks. You could also just shock with chlorine whenever you find you have combined chlorine and not use non chlorine shock at all. As you see there are many ways to shock your spa. I use an inexpensive non chlorine shock that is not buffered because it is less expensive and I use half the product.

[David66]

I don't know if I can turn off the ozonator or not. I know it is not in the control panel, but I might be able to physically unplug the electrical wire to it. I'd have to take the pump cover off and look. This morning at 7:15 am I added 3 ounces of bleach. I started performing your procedure to lower the alkalinity/pH at around 10:30 am. I used Leisure Time test strips, which I've come to find that if you make a mental note of the color after a certain number of seconds after dipping (about 10) it seems to correspond to the Taylor kit results pretty well. At 10:30 the chlorine was about 4ppm. By the time I was done doing the aeration/muriatic acid additions at around noon, the chlorine was reading zero...none...nada. So in about 5 hours my chlorine addition was gone. From what I understand, Dimension 1's implementation of the ozone system is better than most spa manufacturers. Could that have something to do with it?

I did get things "balanced". Using Taylor I arrived at these readings earlier today:

Alk: 100

pH 7.4

CH 270

CYA 45

It's 4pm now and using a test strip, it looks like my pH is sneaking up again. It appears to be around 7.8. I don't really need the Alk to go any lower...should I add an ounce of muriatic acid to lower the pH with jets off?

By the way, according to another message you wrote to me in another thread, you said I would need to add 13 ounces of muriatic acid to get things in order. I'm up to 8 ounces now to get to the numbers above.

I don't know if there's anything in my readings now that could "cause" my chlorine to get used up so fast. I haven't soaked in the tub since New Year's Eve. The water looks nice and clear. I have some foaming when the jets are on high, but I think that's because I had a full tub with people who brought their own suits (technically a no-no, I know, but I don't have a lot of visitors and I don't want to discourage people from visiting with a bunch of hurdles to jump). Before the New Year's Eve session, there was no foaming.

You say below : "most add enough chlorine to get to around 4 ppm FC and then have a little chlorine remaining when they next get in." I guess my tub is bucking the norm when it comes to this. I can add enough chlorine to to 10ppm or more and after a one-person soak (or no soakers) and not have any left 24 hours later, and I would venture to say, a lot less than 24 hours later. I'm also learning from other posts that maybe I'm worrying about maintaining a constant level of free chlorine. As long as I make daily additions (in the morning), and then make additional doses after soaking, combined with the ozonator and vision cartridge, maybe my tub is pretty much always quite safe?

Regarding shocking, will it hurt anything if I simply do a shocking regimen (once a week), even if it isn't needed? I'm willing to "be on the safe side" even if it is a bit on the overkill side. It looks like I need to keep an eye on my CC number...I haven't really done that yet.

Along with that, I didn't have my Taylor kit this summer (which was the first summer for a pool for us, as well). I'll certainly be keeping a closer eye on all the pool readings this coming summer. Last summer was totally nuts with fix-it projects...I was lucky to simply get the thing open and keep the chlorine level in check. I used the chlorine "pills" I like to call them because they look like giant aspirin pills. Trichlor, I suppose. The water was very crystal clear all summer long, though. It's an above-ground pool and was drained for winterizing, so even if the CYA levels are high now, I'll be adding some fresh water when I open it so hopefully that can bring them down a bit. Maybe I'll look into the automatic unit for the pool.

Thanks Richard once again for all your excellent information! I love trying to absorb all the information you write and it has certainly helped me tremendously. Thanks to you I at least now have acceptable pH and ALK levels!

Thanks to Tony for his helpful information as well. I do believe that once I get a system going the maintenance of this thing will become more transparent and I'll be able to enjoy it more.

David

You mentioned you had an ozonator. This could be part of the problem of higher than expected chlorine usage since ozone can actually oxidize chlorine to chlorate thereby using up chlorine faster. It's a delicate tradeoff since an ozonator is also supposed to oxidize organics and if it did this efficiently then chlorine wouldn't have to and chlorine usage would be lessened. It does seem to me from the posts on this form that most ozonators end up causing chlorine usage to increase rather than decrease. So if it is possible for you to turn off your ozonator, you might try that and see if it makes a difference in your chlorine usage. I suspect that at higher CYA levels, the disinfecting chlorine level was lower so it took longer for the ozonator to break it down. Now that you have a lower CYA level and higher disinfecting chlorine level (so that pathogens are killed more quickly), the ozonator is breaking down the chlorine faster.

As for the CYA vs. chlorine, high CYA makes the same Free Chlorine (FC) level less effective so kills pathogens more slowly and breaks down ammonia and organics more slowly. However, chlorine still combines with ammonia very quickly even at high CYA levels so the typical scenario with high CYA is that chlorine usage is still high though perhaps a little lower than at lower CYA, but that Combined Chlorine (CC) shows up. At the lower CYA levels, you don't measure CC as often and pathogens are killed more quickly.

Typical chlorine usage is around 3-4 ppm FC per day for one bather in a hot tub every day in 350 gallons. That seems to be typical of what is seen on this forum where most add enough chlorine to get to around 4 ppm FC and then have a little chlorine remaining when they next get in.

As for automatic chlorine feeders, there are peristaltic pumps available and there is The Liquidator talked about here, but it was designed for pool volumes so I don't know if it would work for a spa -- it would certainly have to be dialed down for fairly low dosing. The main reason that a hot tub is more work than a pool (usually) is that it is such a small volume of water so small changes have larger effects. Also, the bather load is much higher (bathers per water volume) so a hot tub becomes more like a commercial pool with many bathers and that is also more difficult to manage.

In theory, with an ozonator, you shouldn't have to shock at all as the ozonator should be oxidizing organics. Even without an ozonator, if you maintain chlorine levels and keep the cover off for a while after adding chlorine then you shouldn't need to shock very often. Generally, if you don't measure any Combined Chlorine (< 0.5 ppm is OK) then you don't need to shock, though it won't hurt.

By the way, you talk about the ease of maintenance for your pool, but unless you have a saltwater chlorine generator (SWG), then your automatic chlorine feeder is most likely a Trichlor feeder and that is increasing the CYA level in your pool. If you don't use an alagecide (e.g. PolyQuat 60) or a phosphate remover, then you risk getting algae as the CYA level climbs. For every 10 ppm FC added by Trichlor, it also adds 6 ppm to CYA. If instead your feeder is a Cal-Hypo feeder, then this won't increase the CYA level but it will increase Calcium Hardness (CH). For every 10 ppm FC added by Cal-Hypo, it also adds 7 ppm to CH. People who use bleach or chlorinating liquid for their pool add it every day or two unless they have an automatic doser such as The Liquidator I referred to above or unless they have an opaque pool cover (like I have) in which case they add chlorine twice a week.

Richard

[chem geek]

David,

The aeration part of the TA lowering procedure will tend to drive out any volatile chemicals from the water, so not only carbon dioxide, but chlorine will also tend to get outgassed to some extent. So between the ozonator and the aeration you were doing it is not surprising that the chlorine was getting used up rather quickly. The key is whether normal usage (i.e. not running the jets unless you are in the tub) and having the ozonator off results in normal or too high chlorine usage. And yes, removing the electrical connection to the ozonator should do the trick, assuming there's a separate connection for it vs. the pump.

Congratulations on getting things balanced. Even a TA of 100 is on the high side when using bleach so believe it or not you can lower it even more to around 70 or 80. Also keep in mind that aeration (including that done by the ozonator as it is injecting air with some ozone in it into the water and that will bubble out) will cause it to rise so you need to see how the pH goes under normal circumstances of having the jets off, the ozonator off and the cover on. Also, don't worry if the pH is at 7.7 or so, but if it keeps creeping up towards 8.0 then add acid to lower it. Keep us posted on how this goes for you. You should not need to add as much acid to lower the pH at the lower TA, but whenever you add acid be sure to have the circulation pump running -- the jets need not be running and are probably better not to run so you prevent splashing acid (and be sure to add the acid very slowly -- if you want, you can add acid in a bucket of spa water and then slowly add the bucket to the spa).

As for the 13 ounces of acid I said before, that assumed the measurements were accurate so don't sweat it if it doesn't come out exactly the same. I also was targetting a lower TA or 80, not 100, and I assumed you were starting at 225 when you might have already started out a bit lower (and I assumed certain pH, CYA, etc.).

If you aren't even using the tub and the chlorine consumption is high, then I think that either the ozonator is consuming the chlorine or you've got something growing in your tub. My hunch is that its the ozonator which is why turning it off will be a good test.

I agree that you don't have to worry about having a constant chlorine level at all times, but you don't want it to get to zero. Having the ozonator does mean that free-floating pathogens will get killed when they get exposed to the ozone, but this does nothing for pathogens stuck to spa surfaces or in biofilms on such surfaces or to newly introduced pathogens since it takes quite a while for most of the water to have been circulated through the ozonator. So getting to the bottom of this unusually high chlorine usage would be good so that you can more easily ensure you don't get to zero (or near zero -- less than 0.4 ppm FC) chlorine levels at any time. Of course, if it does go to zero, adding chlorine will relatively quickly kill off pathogens, but it can still take minutes depending on the pathogen (not counting really hard-to-kill ones like Giardia and Cryptosporidium).

Shocking with a non-chlorine shock doesn't do anything to pathogens -- it is not a sanitizer. It's sole purpose is to oxidize organics. So it isn't a necessary function the way that FC levels are. I think you should focus on the chlorine usage issue first before worrying about the shock routine. One thing at a time.

For the pool, yes draining will of course eliminate the CYA so that certainly helps. Nevertheless, in my own pool with relatively low chlorine usage of around 0.7 ppm FC per day (due to the opaque pool cover protecting the chlorine from breakdown from UV rays in sunlight) and 1 3" 8-ounce Trichlor tab every 5 days (in 16,000 gallons of pool water) had me get well over 100 ppm CYA in less than a year and a half. I have a cartridge filter so didn't have any dilution from backwashing, but the point is that depending on one's specific situation it may not take long for CYA to build up. With a full drain/refill after a year, as in your case, it probably didn't build up that much even at 2 ppm FC per day usage which may be what you had. For a 6 month season, 2 * 0.6 * 6 * 30 = 216 ppm CYA not counting reduction due to any dilution -- so you can see that it can build up quickly. Having a high CYA with an FC that is too low (specifically, below 7.5% of the CYA level) doesn't guarantee algae, but it increases the risk. If the FC is kept at a minimum of 7.5% of the CYA level (and this is easiest to do by not continually increasing the CYA level) then algae can be kept away by chlorine alone without the need for additional algaecides or phosphate removers (at least up to a phosphate level of 3000 ppb or so). I didn't see algae in my pool with the high CYA because I was also using an algaecide (PolyQuat 60) and might also have had low phosphate and/or nitrate levels, but I found it harder and harder to keep the FC level stable and this may have been that algae was growing (slowly, due to the algaecide) and using up the chlorine even though it wasn't yet visible. That's when I decided to figure out the pool water chemistry, found The Pool Forum website (which no longer accepts new registrations so TroubleFreePool has taken over with many of the same members), and switched to using only chlorinating liquid and no other chemicals.

Richard

[lmartine]

Interesting discussion on high chlorine usage, david66, my sentiments exactly. I too have a 360gal chlorine monster; second fill, using bleach, low CYA, add chlorine in the morning, ozonator running 24/7, etc. My spa went extra green over the past few days, so I tried shocking with 2 cups of 6% bleach and after 2 hours, there was 0 chlorine (I know, I know, test strips bad).

For fun today, I bought some lithium hypo granules (35%chlorine) and did some more shocking. I added the chlorine (dissolved) with the pump on high for 2 or 3 minutes and the air off.

- 8AM no residual, 4 TABLEspoons of lithium, cover off (overcast, not sunny)

- 8:30 AM, measured between 5 and 10PPM, added 2 more tbsp lithium

- 10:30 AM, measure between 3 and 5 PPM, added 2 more tbsp lithium

- 12 noon, measure 5 PPM, added 3 more tbsp lithium

- 12:30 PM, measure 10PPM

- 2:30 PM, measure 5PPM, close cover (lost about an inch of water to evaporation!)

- 9:30 PM measure 0 PPM

So 11 tablespoons of lithium over 4 hours finally got me to 10PPM, but then no residual after 8 hours. The TA also went from 80 to 120 (80 is much better for keeping the pH steady).

I am considering unplugging my ozonator as well, just as a test. This isn't rocket science (voodoo maybe) but the industry people making and selling these things seem to be mostly clueless.

[Chris W]

... I tried shocking with 2 cups of 6% bleach and after 2 hours, there was 0 chlorine (I know, I know, test strips bad).

For fun today, I bought some lithium hypo granules (35%chlorine) and did some more shocking. I added the chlorine (dissolved) with the pump on high for 2 or 3 minutes and the air off.

- 8AM no residual, 4 TABLEspoons of lithium, cover off (overcast, not sunny)

- 8:30 AM, measured between 5 and 10PPM, added 2 more tbsp lithium

- 10:30 AM, measure between 3 and 5 PPM, added 2 more tbsp lithium

- 12 noon, measure 5 PPM, added 3 more tbsp lithium

- 12:30 PM, measure 10PPM

- 2:30 PM, measure 5PPM, close cover (lost about an inch of water to evaporation!)

- 9:30 PM measure 0 PPM

So 11 tablespoons of lithium over 4 hours finally got me to 10PPM, but then no residual after 8 hours. The TA also went from 80 to 120 (80 is much better for keeping the pH steady).

I am considering unplugging my ozonator as well, just as a test. This isn't rocket science (voodoo maybe) but the industry people making and selling these things seem to be mostly clueless.

I know that this could be happening, but that's a lot of chlorine. Unless you are testing with OTO or FAS-DPD based liquid drop kits, you might be bleaching out the reagents and getting false readings.

I did an extra 1/2 tbsp of dichlor in my spa and I hit about 17ppm. Had to aerate uncovered for most of a day to get it back to normal levels.

Also, what's your CYA level? Unstabilized chlorine could be degrading that rapidly due to heat and UV, even if was cloudy.

Chris W

[TinyBubbles]

I got freaked out about high cya levels and decided to try bleach. While my water is still clear, I can tell you that there is a huge difference in the length of time you have a fc residual. With bleach, it goes away fast. After having some friends in the tub, I wanted to make sure I had a good residual for awhile, so I used dichlor again. As suspected, I was able to sustain a good level of fc for a much longer period of time. I'm still in the experimental phase, but I'm considering alternating between the two.

In response to the lithium chloride dosing, it's my understanding that the dosage for this product is in the cup range, not the tbs. range for dichlor dosing. This could explain why it took multiple doses to raise your level to the desired range.

David, I am a newbie too, so perhaps I shouldn't be offereing advice. However, I don't think you need to worry quite so much about having a constant chlorine residual. Especially, since you are using an ozonator and a mineral cartridge. If you are dosing before and after soaks, you should have your bases covered. Many people use a mineral cartridge alone and dose daily with MPS. This is an acceptable form of hot tub sanitization, according to the EPA. You are using a mineral cartridge plus dosing twice daily with chlorine. If you dose after a soak, your chlorine should be killing anything that you introduced to your spa. Here is one thing to consider, many people fill a pitcher with water and put it in their refrierator, taking it in and out when they get thirsty over the course of several days. Granted they aren't soaking in it, but the water is ok on it's own for awhile. Likewise, if you've sufficiently raised your sanitizer level after soaking, your spa should be ok on it's own for awhile. If a constant sanitizer level is very important to you, you might want to consider using bromine, dispensed with a floater.

[chem geek]

You only use 60% more Lithium Hypochlorite by weight or volume than you do Dichlor (see this post for details). It is certainly not a difference between cups and tablespoons unless the Lithium Hypochlorite was significantly reduced in concentration -- it should be around 35% available chlorine.

As for bleach and Dichlor, as I have said before in other posts, the 20 ppm CYA level is conservative. If you go up to 40-50 ppm CYA, then there will be half as much disinfecting chlorine which should still be enough to kill most pathogens quickly but will tend to breakdown or outgas or react about half as fast so should last longer. If instead you found that a SINGLE application of Dichlor lasted longer than a single application of bleach, then that probably has more to do with losses during addition in which case I'd suggest adding the bleach with the jets off and just the circulation pump running to prevent it from outgassing so quickly. It only takes a few seconds for the hypochlorous acid to combine and release from CYA so you just have to get it mixed in the water thoroughly and it should then be more stable.

Richard

[TinyBubbles]

ok, that's a thought, adding bleach with jets off. One concern, someone mentioned that bleach is heavier than water, should I be concerned about it sinking and sitting on the bottom of the spa? That's the main reason that I run the jets when I add it.

[chem geek]

ok, that's a thought, adding bleach with jets off. One concern, someone mentioned that bleach is heavier than water, should I be concerned about it sinking and sitting on the bottom of the spa? That's the main reason that I run the jets when I add it.

Yes, that's a concern so make sure the circulation pump is running and try and add it over a return flow. The easiest thing to do would be to take a bucket of spa water, add the bleach to it, mix it around, then add the bucket back to the spa water with the circulation pump running. That should be diluted enough to not cause any problems and to circulate well. This may all be overkill since the circulation flow without the jets in the spa may be enough to ensure good mixing -- I'm just being conservative about this. The historical problem was with vinyl pools where people would dump bleach or chlorinating liquid in quickly and not near a return flow so the bleach would end up potentially weakening the sides and bottom (since most vinyl pools do not have floor drains). Pouring slowly over a return flow has eliminated that problem.

I'm just sorting this stuff out along with you. The only real way to get to a decent program is through such experimentation to see what works best and is practical. Though I can explain the chemistry side (to some extent), there are many other factors that need to be tweaked through experimentation. Let us know if adding the bleach without the jets helps make it last longer. Also, after a party or when more people have been using the tub then there will be a lot more demand for bleach so possibly the equivalent of 2 ppm FC or so per person, but that's just a guess on my part. Again, experimentation will give you a better sense of typical chlorine demand as a base (i.e. with no one using the tub) plus a per person-hour amount since soak time is a factor as well.

Richard