Chlorine Levels Along With Nature2

[newspaguy]

First let me say thanks for all the experts that have provided so much help with the posts on this site for new spa owners such as myself.

I recently obtained and started up my 1999 Coleman Horizon 408 hot tub which holds approx. 235 gallons or water. After much research on this site and some persuading by friends I went with the Nature2 cartridge system and am following the program recommened by "SPATECh." Im shocking weekly with MPS and adding between 2-3 tsp. of dichlor after each use (usually just 2 people for 30-60 minutes of soaking) After 15 minutes or so of circulating after adding the dichlor I've checked the FC level and its usually between 7-10ppm. Is this too high of a FC limit initially after adding?

And my other concern is by the next day the FC is reading usually 0-1ppm. Should there still be some FC left in the water to keep the spa sanitary or is this normal and okay?

The spa water is crystal clear and my ph and TA are within normal ranges. Does it sound like Im doing everything right or do I need to alter my methods so there is more FC chlorine in the water the day following a soak? Thanks in advance for your help.

[limulus]

I'm also using N2 and dichlor instead of MPS and the recipe states that you should add 1 tablespoon MPS per 250gal before use and again after use. If you look on page 7 of the N2 instructions, it says you can substitute dichlor for MPS and 1 tablespoon dichlor = 3 tablespoons MPS.

3 teaspoons = 1 tablespoon. So if you are adding 3 teaspoons that should be equal to approx 3 tablespoons (according to the info on page 7 of the N2 instructions). Based on your tub volume, I think that is 2 tablespoons to much.

[chem geek]

The N2 instructions aren't quite right in saying that 1 tablespoon of Dichlor is equivalent to 3 tablespoons of MPS. It's true that by weight it takes about 3 times as much MPS as Dichlor to be equivalent, but by volume it's 2 times as much MPS as Dichlor because MPS is denser than Dichlor.

Another problem is that the N2 instructions aren't scaled for the bather load. Obviously more bathers soaking longer requires more oxidizer (Dichlor or MPS). The rough rule of thumb is that every person-hour of soaking requires about 7 ppm FC equivalent in 350 gallons and that's 3-1/2 teaspoons of Dichlor or 7 teaspoons of MPS. Two people soaking for 30 minutes is one person-hour. If the soak is for an hour, then about twice as much oxidizer would be needed, so 2-3 teaspoons is not quite enough, especially if you soak for an hour instead of 30 minutes (also assuming your hot tub temp is close to 104F). You are correct that ideally you will still have at least a small amount of measurable FC the next time you soak as this ensures you are using enough to oxidize all of your sweat and enough to kill bacteria at almost all times (except during part of your soak) though using N2 lowers the risk. If you up your Dichlor amount a bit so you still have at least 1 ppm FC just before your next soak, then you are using enough Dichlor.

Sweat (and urine) use up a lot of chlorine and in a small 235 gallon spa this means the FC level that is required is very high. Just note that by using so much Dichlor, you are going to be building up Cyanuric Acid (CYA) more quickly so will need to change your water more frequently as well -- mostly because of your bather load. The Water Replacement Interval (WRI) is (1/3) x (235) / (2) = 40 days (with hour-long soaks, it's even a shorter interval). How often have you been changing the water? If this is a problem for you, then using bleach instead of Dichlor would have the water last longer, but you'd have a greater tendency for the pH to rise.

Richard

[newspaguy]

The N2 instructions aren't quite right in saying that 1 tablespoon of Dichlor is equivalent to 3 tablespoons of MPS. It's true that by weight it takes about 3 times as much MPS as Dichlor to be equivalent, but by volume it's 2 times as much MPS as Dichlor because MPS is denser than Dichlor.

Another problem is that the N2 instructions aren't scaled for the bather load. Obviously more bathers soaking longer requires more oxidizer (Dichlor or MPS). The rough rule of thumb is that every person-hour of soaking requires about 7 ppm FC equivalent in 350 gallons and that's 3-1/2 teaspoons of Dichlor or 7 teaspoons of MPS. Two people soaking for 30 minutes is one person-hour. If the soak is for an hour, then about twice as much oxidizer would be needed, so 2-3 teaspoons is not quite enough, especially if you soak for an hour instead of 30 minutes (also assuming your hot tub temp is close to 104F). You are correct that ideally you will still have at least a small amount of measurable FC the next time you soak as this ensures you are using enough to oxidize all of your sweat and enough to kill bacteria at almost all times (except during part of your soak) though using N2 lowers the risk. If you up your Dichlor amount a bit so you still have at least 1 ppm FC just before your next soak, then you are using enough Dichlor.

Sweat (and urine) use up a lot of chlorine and in a small 235 gallon spa this means the FC level that is required is very high. Just note that by using so much Dichlor, you are going to be building up Cyanuric Acid (CYA) more quickly so will need to change your water more frequently as well -- mostly because of your bather load. The Water Replacement Interval (WRI) is (1/3) x (235) / (2) = 40 days (with hour-long soaks, it's even a shorter interval). How often have you been changing the water? If this is a problem for you, then using bleach instead of Dichlor would have the water last longer, but you'd have a greater tendency for the pH to rise.

Richard

Chem geek,

So then based on the volume of my tub (235 gal) how much dichlor would you recommend per person hour of soaking? You said 2-3 tsp is not enough, so how much should I up my usage after a soak? And at what level of CYA should I change the water? Im terrible at converting numbers and I tried based on your calculations for a 350 gallon tub, but didn't do well. Your help is appreciated.

This was my first fill for this tub, so would I be better off using a different sytems such a bromine at the next water change due to the smaller water volume, or will I have similar issues?

Thank you,

Geoff

[chem geek]

Chem geek,

So then based on the volume of my tub (235 gal) how much dichlor would you recommend per person hour of soaking? You said 2-3 tsp is not enough, so how much should I up my usage after a soak? And at what level of CYA should I change the water? Im terrible at converting numbers and I tried based on your calculations for a 350 gallon tub, but didn't do well. Your help is appreciated.

This was my first fill for this tub, so would I be better off using a different sytems such a bromine at the next water change due to the smaller water volume, or will I have similar issues?

Thank you,

Geoff

For one person-hour which is two people soaking for 30 minutes, that's 3-1/2 teaspoons of Dichlor (regardless of tub size) so try using that and see what sort of an FC residual you end up with just before your next soak. If you soak for 60 minutes, use more Dichlor -- perhaps up to 7 teaspoons and see how that goes. These are just guidelines -- you can tweak based on your actual residual FC numbers before the next soak.

As for the CYA level, that's a hard question to answer since it depends on your goals. Many people don't worry about it and just change the water when it seems to start turning. In some tubs, the CYA level seems to not climb as much as others, even with similar chemical additions (we don't know why for sure -- perhaps some oxidation of CYA by chlorine). The WRI is a standard guideline, but you can just see how your water does over time. If you weren't using N2, then I'd be more concerned about the high CYA level in terms of sanitation, but the N2 acts a bit as an insurance policy though it's not the same as maintaining a more consistent FC/CYA ratio. If you find that the water turns bad more quickly then you'd like, then you can consider using bleach after one initial week of Dichlor, but would then need to manage the pH more carefully.

As for how to manage a smaller tub, using chlorine is fine -- you don't have to use bromine (on your next water change) unless you want to. The main advantage to bromine is ease-of-use due to a floating feeder so you don't have to remember adding sanitizer every day. It's more expensive, however, though for a hot tub it's not that much. It's really up to you, but there's nothing wrong with using chlorine. Technically, you'd still need high levels of bromine just as you would with chlorine (or would need MPS shock) -- basically you need an amount of chemical to oxidize your sweat.

Richard

[newspaguy]

Chem geek,

So then based on the volume of my tub (235 gal) how much dichlor would you recommend per person hour of soaking? You said 2-3 tsp is not enough, so how much should I up my usage after a soak? And at what level of CYA should I change the water? Im terrible at converting numbers and I tried based on your calculations for a 350 gallon tub, but didn't do well. Your help is appreciated.

This was my first fill for this tub, so would I be better off using a different sytems such a bromine at the next water change due to the smaller water volume, or will I have similar issues?

Thank you,

Geoff

For one person-hour which is two people soaking for 30 minutes, that's 3-1/2 teaspoons of Dichlor (regardless of tub size) so try using that and see what sort of an FC residual you end up with just before your next soak. If you soak for 60 minutes, use more Dichlor -- perhaps up to 7 teaspoons and see how that goes. These are just guidelines -- you can tweak based on your actual residual FC numbers before the next soak.

As for the CYA level, that's a hard question to answer since it depends on your goals. Many people don't worry about it and just change the water when it seems to start turning. In some tubs, the CYA level seems to not climb as much as others, even with similar chemical additions (we don't know why for sure -- perhaps some oxidation of CYA by chlorine). The WRI is a standard guideline, but you can just see how your water does over time. If you weren't using N2, then I'd be more concerned about the high CYA level in terms of sanitation, but the N2 acts a bit as an insurance policy though it's not the same as maintaining a more consistent FC/CYA ratio. If you find that the water turns bad more quickly then you'd like, then you can consider using bleach after one initial week of Dichlor, but would then need to manage the pH more carefully.

As for how to manage a smaller tub, using chlorine is fine -- you don't have to use bromine (on your next water change) unless you want to. The main advantage to bromine is ease-of-use due to a floating feeder so you don't have to remember adding sanitizer every day. It's more expensive, however, though for a hot tub it's not that much. It's really up to you, but there's nothing wrong with using chlorine. Technically, you'd still need high levels of bromine just as you would with chlorine (or would need MPS shock) -- basically you need an amount of chemical to oxidize your sweat.

Richard

Richard,

Im interested in trying the unscented bleach method that you referred to. I just spent 2 hours looking through the old posts to find exactly how do use the bleach method without much luck other than seeing several references to the method. Im assuming I would just add it after soaking like I'm doing with the Dichlor. How much bleach do you use per person hour of soaking? Do you still continue to shock weekly with MPS with the bleach method?

[chem geek]

Richard,

Im interested in trying the unscented bleach method that you referred to. I just spent 2 hours looking through the old posts to find exactly how do use the bleach method without much luck other than seeing several references to the method. Im assuming I would just add it after soaking like I'm doing with the Dichlor. How much bleach do you use per person hour of soaking? Do you still continue to shock weekly with MPS with the bleach method?

I just want to reiterate that with your N2 system you're not in as bad a shape of using Dichlor-only if you wanted to. That is, the metal ions from the N2 help compensate for the lower sanitation levels from the lower effective chlorine concentration over time as the CYA builds up, though this isn't a perfect substitution since the chlorine kills much faster than the metal ions.

Anyway, to use the bleach method, after a fresh refill you initially use Dichlor to cumulatively add around 20 ppm CYA. With Dichlor, for every 10 ppm FC that is added, it also increases CYA by 9 ppm. So basically in your situation with 2 people soaking for 30 minutes with you're adding 3-1/2 teaspoons of Dichlor in your 235 gallons, you're adding around 10.4 ppm FC and 9.5 ppm CYA per day. After 2-3 days of using Dichlor you'll have enough CYA and can then switch to using bleach after that -- I'd say, just switch after 3 days of Dichlor. The amount of bleach to add that is equivalent to 3-1/2 teaspoons of Dichlor is 5 fluid ounces (for 6% unscented bleach). You would adjust the amount as needed so that you have a small residual FC just before your next soak.

Using bleach in such a small tub can have the pH go up quite a lot after you add the bleach so I would recommend having an additional pH buffer to help keep the pH in line. The best pH buffer would be to use borates by adding boric acid to the water. This is found in products such as Leisure Time pH Balance Plus (a 3 pound jar is $19) or a 1 pound jar of Boric Acid for $5 from The Chemistry Store here. It takes 9 ounces weight (about 5 fluid ounces volume) of Boric Acid to add 50 ppm to your 235 gallon spa. If you add the pure Boric Acid, it will lower the pH somewhat, but not that much (from around 7.5 to 7.2), but if you use the Leisure Time pH Balance Plus product, then the pH should not drop upon addition.

Even with the pH buffer, you may find the pH will rise over time so will need to add acid periodically to lower the pH. Just check the pH before you soak every day until you get a feel for how the pH moves -- you'll also check the Total Alkalinity (TA) to make sure it doesn't go below 60 ppm over time. To minimize this pH rise effect, you'll want the Total Alkalinity (TA) to be lower so don't increase it above 60 ppm after you're fresh refill (it might already be above 60 ppm from your tap water in which case just leave it as is). Worst case, if the pH rise is too annoying for you, you can always go back to using Dichlor.

Richard

[tony]

Richard,

Im interested in trying the unscented bleach method that you referred to. I just spent 2 hours looking through the old posts to find exactly how do use the bleach method without much luck other than seeing several references to the method. Im assuming I would just add it after soaking like I'm doing with the Dichlor. How much bleach do you use per person hour of soaking? Do you still continue to shock weekly with MPS with the bleach method?

I have been using the unscented bleach method for some time now. I add after soaking like I do with dichlor and shock weekly with MPS. I generally add a little dry acid once a week to keep my pH in check

Like any other chlorine, the amount to use after soaking has more to do with the free chlorine level and your spa demand. Every spa will be different. You should add enough chlorine to bring your FC level to 3+ ppm. Test in the beginning and you will get the "feel" of your spa. My spa is 485 gallons and three oz generally gets my FC level high enough. Add some on off days. Don't skip more than a couple of days.

[limulus]

Hey Guys,

I see you mention the addition of dichlor and then switching over to bleach, which is of interest to me also. However, I see no mention of the pre and/or post dosage. The N2 recipe says to add before and after soaking. Are you doing this or only after? I'm currently adding 2 tsp dichlor before and after. I also pre-shocked with 3 tbs dichlor and this brought the FC up to 10ppm.

[tony]

Hey Guys,

I see you mention the addition of dichlor and then switching over to bleach, which is of interest to me also. However, I see no mention of the pre and/or post dosage. The N2 recipe says to add before and after soaking. Are you doing this or only after? I'm currently adding 2 tsp dichlor before and after. I also pre-shocked with 3 tbs dichlor and this brought the FC up to 10ppm.

I add after I soak. This way I soak in water with a very low free chlorine level.

[limulus]

Thanks Tony,

Pre-soak, I add 2tsp, I let it mix 15-20min and then measure FC. It normally comes in around .5ppm just as the N2 recipe states. We soak and then I add another 2-3 tsp after we're done. We also have a copper ionizer and keep that at .3ppm. I don't recall seeing anything in the N2 manual about raising FC to 3.0ppm. If I'm shocking, I add 3 tbs and that brings it up to 10ppm in our 488g tub.

[tony]

I don't recall seeing anything in the N2 manual about raising FC to 3.0ppm.

No you won't find it there. It comes from the "Vermonter" method of sanitiation. You can find it at the FAQ section of the rhtubs.com forum. Vermonter is a microbiologist who used to regularly post on that forum. He used his HotSpring Grandee to test his water and came up with his recipe to keep a very sanitized spa including the use of N2. I personally put a lot more faith in Vermonters experiments than in anything N2 puts in their manual or on their website.

If, by chance, you head over to rhtubs.com, check out Northmans routine also. It originates from the Vermonter method but elaborates a bit more to include total tub maintenance. All good reading for new spa owners who want a good understanding of this type of sanitation.

[Nitro]

I have been using the unscented bleach method for some time now. I add after soaking like I do with dichlor and shock weekly with MPS. I generally add a little dry acid once a week to keep my pH in check

Tony, you need to add acid and you're using MPS? I used MPS one time and it lowered my TA/PH too low. I actually had to add baking soda, first time ever. I have my PH tuned pretty well, to where I rarely need to add acid. It's been over three weeks now.

[limulus]

Thanks again Tony. I thought I had read everything over at rh. Looks like I have a new assignment.

[tony]

Thanks again Tony. I thought I had read everything over at rh. Looks like I have a new assignment.

Now just substitute bleach for dichlor and you have the Vermonter/chem geek method of sanitation.

If I recall, I believe Richard (chem geek) had spoken to Vermonter a while back.

[chem geek]

Thanks again Tony. I thought I had read everything over at rh. Looks like I have a new assignment.

Now just substitute bleach for dichlor and you have the Vermonter/chem geek method of sanitation.

If I recall, I believe Richard (chem geek) had spoken to Vermonter a while back.

The Vermonter and Northman methods are similar in that they both use Dichlor only -- neither are the "Dichlor for a week, then switch to bleach until the next refill" method that I proposed. I did communicate (via E-mail) to Vermonter a while back but we never got to a consistent conclusion. He was going to send me some detailed bacteriological data (CT values, etc.) but I never got that (he probably got busy). So I would not say that he agrees with me, though I don't think he disagrees either. He may just believe that Dichlor only is OK in practice given what he measured in his own spa not seeing bacterial counts of any consequence.

My take is that one person's measurement isn't enough and that it's more of a statistical probability thing where Pseudomonas could take hold in those later months of soaking at higher CYA levels. It might be that keeping a very rigorous regimen with measurable FC at all times will be OK, but there's not much room for error. With the Dichlor then bleach approach, the level of disinfection is consistent month-to-month so a short-term slip-up is more likely to be rectified due to the still-high disinfection level. At least that's my best guess. You also get the benefit of water that seems to last longer before "turning" as it seems to do when the CYA levels climb (I think that may have more to do with the slower oxidation rates at higher CYA levels without raising the FC proportionately).

Remember that there are LOTS of people using the Dichlor-only approach without problems, but I'm focused on those cases that don't work to try and minimize the chances of getting hot tub itch/rash/lung and for a logically more consistent approach in terms of disinfection and oxidation rates.

Richard

[tony]

With the Dichlor then bleach approach, the level of disinfection is consistent month-to-month so a short-term slip-up is more likely to be rectified due to the still-high disinfection level. At least that's my best guess. You also get the benefit of water that seems to last longer before "turning" as it seems to do when the CYA levels climb (I think that may have more to do with the slower oxidation rates at higher CYA levels without raising the FC proportionately).

I have found this to be true in my spa.