Jump to content
Nitro

Dichlor/bleach Method In A Nutshell

Recommended Posts

With that kind of bather load, it might take longer to fully oxidize the bather waste. It's best to check 24 hours later. Even so, it does seem that perhaps you used more than needed. The teaspoons of MPS would have been excess given the amount of bleach you used.

Anyway, the amount of FC for 8 person-hours in 340 gallons is 55 ppm or so. So ending up with 13 ppm is not as far off as it might seem. You clearly needed almost 80% of the amount you added. See how it reads around 24 hours after you added the bleach. Then if you want to adjust your dosing formula somewhat, you can do that, but it doesn't sound like it needs that much adjustment and that the rule-of-thumb is close in a rough sense.

If you were soaking for 2 hours, then I doubt very much that the spa was hot at 104ºF which is the assumption used for the bather-load "rule". At lower water temps, you sweat less, so it's not surprising that you don't need to use as much oxidizer after a soak. Let us know the FC after 24 hours since the dosing and let us know the water temp during the 2-hour soak. We can then have some sort of rough factor for lower water temps.

Share this post


Link to post
Share on other sites

Never got a chance to check at 48hours with all the wind and rain. Did however check it at 72 hours and was down to 1.4ppm.

What is the rule of thumb for use of MPS. I don't think I'm clear on how to use it effectively or at the right time.

Use the four bather scenario above I added two teaspoons thinking it would help maintain sanitization levels by not having the chlorine do all the work. Was that a misleading assumption?

Share this post


Link to post
Share on other sites

See my earlier post in this thread where I give the amount MPS needed if you were to use only MPS (I also list Dichlor and bleach amounts if you were to use only one of those).

There is no need to use MPS since it does not do a better job than chlorine and it's much more expensive. The only time MPS is usually used in spas is with Nature2 for people who don't want to use chlorine, at least most of the time.

In your scenario, you already added enough chlorine to oxidize the bather waste so the MPS was unneeded extra on top of that. The 2 teaspoons of MPS would have handled 2/7th of a person-hour or around 17 minutes of one person soaking so not very much of the total oxidizer demand you had. The amount of MPS you used of only 2 teaspoons is equivalent to 2 ppm FC in 340 gallons. So given the extra 2 days of FC drop and where you ended up, I'd say that the bleach amount was approximately correct and the MPS was just a little extra to have some chlorine leftover after 2 extra days, assuming you started your soak with around 1-2 ppm FC.

Note that when using chlorine manually dosed, you need to add it every day or two unless you dose much higher. As you saw, after 3 days you would have nearly run out had you not added extra oxidizer. This is why chlorine works best for those using the tub every day or two. Those that use it only once or twice a week (especially if they have an ozonator since that uses up more chlorine when there is low bather-load) often find bromine to be easier since it has bromine tabs that release a constant background level of bromine or people use a saltwater chlorine generator for a similar purpose for chlorine.

Share this post


Link to post
Share on other sites

Okay... I am using the dichlor / bleach method and Do check it everyday and add about 2 oz of 8.5% bleach depending on my test results. This is what confused me:

Add MPS before/during high bather loads to help out the Chlorine, and keep CD low. (Optional but recommended)

So tonight, we have a couple coming over and will be in it a little more / longer than usual. So do I up the FC at the beginning or throw in some MPS? Just trying to tweak the final step... Sorry if I am misunderstanding you...

Thanks...

Scott

Share this post


Link to post
Share on other sites

Yeah, there are some things in the original post by Nitro that I disagree with. MPS is optional, but I would not say recommended unless one is having a problem with chlorine demand. You can first see how things go with chlorine alone. He also says that borates are optional, but I would say they are recommended along with low TA in order to keep pH more stable.

Also, MPS has a minor persulfate component that can be irritating and while it is removed in the presence of silver ions as with Nature2, it persists longer in a spa without such silver ions. So I wouldn't use it unless you have to and not at the start of the soak. Just start off with a Free Chlorine (FC) level. Now as for what level to start with, that's up to you. 1-2 ppm FC will not result in noticeable smell, but it will most certainly run out during the soak. Since you will be blasting with chlorine right after the soak, you will prevent uncontrolled bacterial growth and biofilm formation, but during your soak you will only have a modest amount of disinfection during the earlier part of your soak from the monochloramine that results from the chlorine combining with bather waste.

If you were a commercial/public spa or thought the other couple was unhealthy, then you would try and maintain an FC level at all times during the soak, but that becomes pretty impractical with the person-hours you have in your sized spa. You could raise the FC to start with to something on the order of 15-20 ppm or so to not run out during the 2 hours of soaking (the rest of the FC gets used up afterwards), but that will be noticeable in smell and even with CYA in the water it would be noticeably strong (note that the EPA FC limit for spas is 5 ppm, though that doesn't account for CYA). In a real commercial/public spa with a chlorine feedback system, it would add more chlorine continuously as needed, but without CYA in the water it too usually ends up smelling and noticeably oxidizing skin and swimsuits. Most people with residential spas just start out with a low FC level. If you want, you can start out with something more like 3-5 ppm instead of 1-2 ppm. You may notice this somewhat early in the soak, but probably not later and it will provide more monochloramine that may last through the soak. It would be interesting for you to measure FC and CC right after your soak before you add more chlorine (I suspect that you'll have 0 FC and that your CC will be close to your original FC amount, but I'd like to verify that).

Just so you know, your spa usage is pretty extreme in terms of bather load, at least for a residential spa.

Share this post


Link to post
Share on other sites

I checked FC and it was zero. We had the other couple over and only soaked for an hour at 101. I added only 10 oz of 8.5% bleach. No MPS at all from now on.

Why is my usage extreme? The hours of soaking? We usually run the jets for about half the time we are in and just sit and talk the rest.

During the week if we get in it, we are in for about 20-40 minutes with two to four of us depending on if the kids join us.

Share this post


Link to post
Share on other sites

I would have expected the FC to be 0 right after the soak before you add more chlorine, but what was the CC? If you didn't check that this time, check it next time. Again, just out of curiosity (verifying that my assumptions are correct).

Yes, having four people for two hours as you did earlier is quite high. It's more common to have 1-2 people for no more than 1 hour and usually less if the water is hotter (104ºF). 4 people is higher and 2 hours is much higher. Doing that every day also makes this higher than typical bather load, though that sounds like that's not the case for you. This isn't a problem and is handled by using more chlorine proportionate to the person-hours, but it is something some people have trouble with if they only think to add smaller amounts of chlorine because they are frightened about the high FC when you add the chlorine (55 ppm FC for the earlier 8 person-hours in your sized tub).

So you soaked for one hour with 4 people so 4 person-hours would need 4*5 = 20 fluid ounces of 6% bleach or 14 fluid ounces of 8.5% bleach (are you sure it isn't 8.25%?) if the water temp was hot, but yours is less than 104ºF. So just measure the FC before your next soak and if it's too low or high then adjust your dosing after your soaks accordingly. It sounds like you may have dialed in what is needed pretty well.

Don't worry about your higher bather-load. You are on top of it. Just so you know, if you had 2 people for an hour and 4 people for 2 hours on the weekend and then an average of 3 people for 30 minutes every day during the week, then that would be 2*1+4*2+3*(30/60) = 11.5 person-hours per week. With Dichlor-only, the standard Water Replacement Interval (WRI) gives a rough idea of how long the water lasts:

WRI = (1/3) x (Spa Size in Gallons) / (# of Bathers per Day)

where this presumes 20 minute soaks so in person-hours this is

WRI = (1/9) x (Spa Size in Gallons) / (# of person-hours per day)

so with my example of your usage this is (1/9) x (340) / (11.5/7) = 23 days

So you'd be changing your water every 3-4 weeks. With Dichlor-then-bleach you should be able to go at least twice as long between water changes so around 1-1/2 months or more and when you do change the water you'll notice that its quality wasn't that bad when you changed it (especially compared to Dichlor-only usage). This is because with Dichlor-then-bleach you avoid the buildup of Cyanuric Acid (CYA) that reduces chlorine effectiveness to the point where it doesn't oxidize bather waste quickly enough. You will probably want to use some Dichlor for one day every month (for a mid-week soak) to keep the CYA stable since it slowly drops over time and with your spa usage and high chlorine levels after a soak, the CYA might be dropping somewhat faster than in other spas. Let us know how things go since your high bather-load is a good example for making sure our assumptions and calculates are as good as they can be.

Share this post


Link to post
Share on other sites

Probably too long after the fact and used in between, but my FC tonight .2ppm and my CC was 1.8ppm. I'll get a better reading next time. My CC is really high isn't it?

Share this post


Link to post
Share on other sites

It seems that you didn't add enough chlorine after the last soak (I had calculated you needed closer to 14 ounces while you added only 10). When that happens, you can get low FC and measurable CC. So add some chlorine now -- I'd say around 5 ppm should be OK and if you soak again tonight then add more after your soak. See what you get tomorrow morning. If the FC is very low again, then add 10 ppm FC worth since perhaps you've gotten behind.

The usual pattern for FC and CC from just before a soak through to the next soak goes something like the following (this is for a roughly 3 person-hour bather-load):

Before Soak ....... During Soak ......... Adding Chlorine and then Time Between Soaks Until Next Soak

FC: .. 2 ............... 1 ... 0 ...... 0 .......... 20 ........ 15 ......... 10 ......... 6 ......... 4 ........ 3.5 ........ 3 ....... 2.5 ..... 2

CC: .. 0 ............... 1 ... 2 ...... 2 ........... 2 .......... 5 ........... 8 ......... 4 ........ 2 ......... 1 .......... 0.5 ....... 0 ...... 0

If you have high bather-load, then you can get behind, especially if you soak twice in one day. In that case, you may have more lingering CC.

Share this post


Link to post
Share on other sites

I apologize if this has been covered. If you've been successfully using the Dichlor/Bleach method but need to take a trip away from home for a week or more is there anything you can do (besides having some come over, check, and add chlorine daily) to keep the sanitizer level in a healthy range?

Share this post


Link to post
Share on other sites

I just started using the dichlor/bleach method for the first time. I used dichlor for the first week then added borax, bleach and Lo' N Slo ( Spaguard) to lower the PH for the rise from the borax. My hot tub is 320 gallons. So I added 3 cups of borax which was equivalent to 24 oz I believe. The PH went above 8.2 so I have been adding the Lo' N Slo for the past 3 dayz to bring down the PH but it's still above 8.2. I didn't have the other acid that was suggested. I'm wondering if the Lo'N slo (sodium bisulfate) will work in this case and approx. how much I will need to counteract the 3 cups of borax. Also my wife came out of the tub yesterday and has a rash today. Would that be from the high PH or is there other factors. The chlorine levels are fine.

Share this post


Link to post
Share on other sites

I apologize if this has been covered. If you've been successfully using the Dichlor/Bleach method but need to take a trip away from home for a week or more is there anything you can do (besides having some come over, check, and add chlorine daily) to keep the sanitizer level in a healthy range?

If it's only 1 week, you can usually shock with chlorine (to at least 10 ppm), lower the water temp (no higher than 80ºF) and the chlorine will probably last that long. This assumes you have some CYA in the water already so it's not a fresh refill. If you're talking longer than 1 week, then someone needs to put more chlorine in at least once a week (to shock level, if only once a week).

Share this post


Link to post
Share on other sites

I just started using the dichlor/bleach method for the first time. I used dichlor for the first week then added borax, bleach and Lo' N Slo ( Spaguard) to lower the PH for the rise from the borax. My hot tub is 320 gallons. So I added 3 cups of borax which was equivalent to 24 oz I believe. The PH went above 8.2 so I have been adding the Lo' N Slo for the past 3 dayz to bring down the PH but it's still above 8.2. I didn't have the other acid that was suggested. I'm wondering if the Lo'N slo (sodium bisulfate) will work in this case and approx. how much I will need to counteract the 3 cups of borax. Also my wife came out of the tub yesterday and has a rash today. Would that be from the high PH or is there other factors. The chlorine levels are fine.

You don't mention your Total Alkalinity (TA) level. You should lower that before adding the borates (because it's easier to lower). The Pool Calculator says that for 320 gallons you get to 50 ppm Borates using 19 ounces weight (18 ounces volume) of 20 Mule Team Borax and for acid it takes 9 ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) where that amount is equivalent to 12 ounces weight (8 ounces volume) of dry acid. You should have added HALF the Borax and HALF the acid, then repeat with the second half. Your pH is probably MUCH higher than 8.2 (probably around 9.0) so not only is this possible to be irritating, but you could have caused scaling in your tub or the heat exchanger of your spa heater.

So, 3 cups of Borax was too high, though not terribly so, but would require 15.7 ounces weight (10.5 ounces volume) of dry acid to compensate for the pH. You probably didn't add enough dry acid.

Share this post


Link to post
Share on other sites

I apologize if this has been covered. If you've been successfully using the Dichlor/Bleach method but need to take a trip away from home for a week or more is there anything you can do (besides having some come over, check, and add chlorine daily) to keep the sanitizer level in a healthy range?

If it's only 1 week, you can usually shock with chlorine (to at least 10 ppm), lower the water temp (no higher than 80ºF) and the chlorine will probably last that long. This assumes you have some CYA in the water already so it's not a fresh refill. If you're talking longer than 1 week, then someone needs to put more chlorine in at least once a week (to shock level, if only once a week).

Thank you Chem Geek! Most helpful indeed!

Share this post


Link to post
Share on other sites

I should note that a shock level of chlorine will only last one week if there is no ozonator. With an ozonator, chlorine demand with no bather load is often doubled or more. A comparison of chlorine levels assuming a 25% loss without an ozonator vs. a 50% loss with an ozonator is shown below starting with 10 ppm FC:

DAY .. FC @ 25% .. FC @ 50%

.. 1 ......... 10 ............... 10

.. 2 ......... 7.5 .............. 5.0

.. 3 ......... 5.6 .............. 2.5

.. 4 ......... 4.2 .............. 1.2

.. 5 ......... 3.2 .............. 0.6

.. 6 ......... 2.4 .............. 0.3

.. 7 ......... 1.8 .............. 0.2

.. 8 ......... 1.3 .............. 0.1

.. 9 ......... 1.0 .............. 0.0

10 .......... 0.7 .............. 0.0

11 .......... 0.6 .............. 0.0

12 .......... 0.4 .............. 0.0

13 .......... 0.3 .............. 0.0

14 .......... 0.2 .............. 0.0

If you lower the water temperature (say to 80ºF), then the no ozonator loss is lower than shown above and it might be possible to go 2 weeks (the loss with an ozonator is still substantial since the part of the loss due to ozone reacting with chlorine doesn't change much since it's slower but still reacts). It also depends on the age of your water since a buildup of slow-to-oxidize organics can have the chlorine demand go up.

Share this post


Link to post
Share on other sites

Okay ChemGeek - I know you like data and I've never been able to provide 24 hours results so I thought I'd give you some feedback.

Jacuzzi J345 w/ ClearRay 340 gallons

I had the tub balance after a fresh fill last weekend using SeaKlear Spa Flush:

TA 50

pH 7.6

I added .8oz (10ppm) dichlor. Next day FC was 7.6 after sitting 24 hours. Two days after that I added 12oz of Gentle Spa and my TA shot up to 70 and pH 8.0+.

Dialed it down to:

TA 50

pH 7.6

My wife and I used the tub Friday night for 30 minutes (2.4 FC before using tub) - we were losing about 24% every day without sing the tub and no ozone. We put in 3.5tsp (7ppm) dichlor and check it Saturday night and it was 3.6ppm. We added .2 oz (2.3ppm) to get us to 6.0ppm because we had another couple coming over.

4 of us used the tub at 102F for one hour - I added 7 tsp of dichlor (14ppm) and 7oz of 8.25% bleach because at the last 14 ppm it put me at about 30ppm CYA calculated.

So, I checked the FC 22 hours later, not quite 24, but the FC was 13.6ppm and my CC was .4. So we upped the tub to 6ppm and used it for an hour and then added 28ppm (7ppm x4 soaking hours).

Did the bleach make the FC stay high or maybe not need as much?

Edit:

Monday nights numbers(24 hours after last set)

TA 50

pH 7.4

FC 9.0

CC .4

Share this post


Link to post
Share on other sites

Thank you so much for the detailed analysis.  Yes, it would seem that you could somewhat less chlorine than what I've been recommending as a guideline.  The following is an analysis of your results.  7 ppm FC in 350 gallons would be 7.2 ppm FC in 340 gallons so we'll use that as a reference per person-hour.

Initial FC . Person-Hours .. Ending FC .. FC per Person-Hour (in 340 gallons)

... 9.8 ............... 0 .................. 7.6 ................ N/A (22% loss)

2.4+7.1 ............ 1 .................. 3.6 .................... 5.9

6.0+28.4 .......... 4 ................ 13.6 .................... 5.2

6.0+28.0 .......... 4 .................. 9.0 .................... 6.3

It may be that you are cleaner than others or that the temp is slightly lower (though 102 is pretty close to 104) or that you've got less aeration that might outgas some chlorine or that my earlier average of reports was off or too conservative.  At any rate, it's just a guideline and the real rule is to add enough chlorine so you still have a residual by the start of your next soak.

Share this post


Link to post
Share on other sites

One thing I forgot to ask... You still shock the tub once a week with bleach to 12 ppm (even if you added say 14ppm from two people soaking for an hour) correct?

I don't see it listed here but I think I seen it in one of the other threads... Just checking...

On a side note - we did have less aeration that night... We didn't use the air features at all, just the waterfall and jets, no air.

Share this post


Link to post
Share on other sites

If you are properly maintaining FC to not get to zero so are using enough after each soak, then there should be no need to shock ever.

Share this post


Link to post
Share on other sites

<p>chem geek, i see when you analyzed Orion's number you speculated that you estimates for chlorine addition may have been high.

I wanted to ask if you think the "ClearRay" UV system that he stated is in his tub could have any bearing on this.

I see it has been discussed that Ozone will eat up higher levels of free chlorine, would the UV system be beneficial in this aspect ?

Share this post


Link to post
Share on other sites

I wanted to share some data i have been collecting from my Jacuzi j-480 with the UV system. The tub is just now a week old.

I have been adding about 0.4oz (2tps) of diChlor each night after our 2 person 30min soak.

Tues(before soak) = 0.5 FC (tub last used on Sunday)

Tues (after soak & adding 2 tsp dichlor)= no test done

Wed (before soak) = 1.4 FC and 0.4 TC

Wed (after soak& adding 2 tsp dichlor) = 5.0* FC and 0.5* TC

Thur (before soak) = 2.2 FC and 0.2 TC

Thur (after soak) = 1.4 FC and 0.4 TC

Thru (after soak & adding 2tsp dichlor) = 4.4 FC and 0.4 TC

I am up to 39oz (33ppm FC) of DIchlor added - should be gettig close to 30ppm CYA

All testing done with taylor FAS-DPD using 25ml samples.  (*=10ml test)

Share this post


Link to post
Share on other sites

Something I've noticed, and at this point it's purer speculation with a hint of data and little hypothesis.

Above I was using about 22% Of bleach a night. Lately I've jumped to 50% (tonight i went from 2.4' last night to .6 tonight) with less tub usage - maybe once a week or every 10 days. Water is crystal clear, no odor, no nothing. I checked CYA on 1/1 and it dropped to 20 and about a week or so earlier I added Dichlor to bump it because it was 20-25. So what kills CYA so quick? UV - like the sun... or the ClearRay UV! When I put in the dichlor "bump" every 10 days or so it reduces to it to about 30% usage daily.

My assumption, and I post about every 2 days worth of numbers (I keep a book when I test), is that the ClearRay UV is burning up the CYA.

I'd be curious to know if anyone else is seeing this phenomenon...

Share this post


Link to post
Share on other sites

We do know that hot spa temperatures will accelerate the natural oxidation of CYA by chlorine (see the second part of the first post in the thread http://www.troublefreepool.com/degradation-of-cyanuric-acid-cya-t8880.html'>Degradation of Cyanuric Acid (CYA)) and that this seems to be roughly at a rate of around 5 ppm CYA per month, at the recommended CYA levels. Now UV does break down chlorine into hydroxyl radicals and the UV might break down CYA though the UV in sunlight doesn't seem to (the UV in the ClearRay system is at a lower and stronger frequency that CYA absorbs more strongly and *might* break down).

What I find interesting is that your chlorine loss rate goes up when the CYA level goes down. That actually makes sense because the active chlorine level goes up when the CYA level goes down (when comparing the same FC levels) so chlorine will react that much faster and outgas that much faster and get broken down by UV faster so have a higher apparent loss rate. It does seem that in your situation you'll need to use Dichlor more frequently than just once a month, but you'll still use bleach most of the time.

If you have a way of turning off your ClearRay UV system, then your experiments could be more definitive and it would be useful info for us to know.

Share this post


Link to post
Share on other sites

I just did a flush drain and refill on my tub (5 weeks old) yesterday. I will have to check my CYA levels this time after a few weeks as I did notice my bleach usage had started to go up as well.

One thing I was shocked at the amount of "gunk" that came out on the flush after just 5 weeks of usage. I never once during that time let chlorine get below 0.0

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...