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Dichlor/bleach Method In A Nutshell

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So you used Spa System Flush originally, then used the tub with chlorine with levels always maintained, then used Spa System Flush again for the next refill and you found a lot of gunk come out? It's probably lotions and oils that chlorine doesn't break down, but that usually would get caught in the filter. If you used the flush with the filter removed (as directed), then it is surprising that you found a lot of gunk.

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So you used Spa System Flush originally, then used the tub with chlorine with levels always maintained, then used Spa System Flush again for the next refill and you found a lot of gunk come out? It's probably lotions and oils that chlorine doesn't break down, but that usually would get caught in the filter. If you used the flush with the filter removed (as directed), then it is surprising that you found a lot of gunk.

It was a brand new tub, no flush on the first fill. So the flush got stuff that had been in there factory I'm sure.

After this first refill, 9.0 FC with dichlor and about 20 hours later 6.0FC, 30% baseline demand with no CYA yet. Is that ok?

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My J345 was the same way. I used SeaKlear and couldn't believe it. Water was always crystal clear even when I changed the water, but I did the one month change to rid the tub of gunk from manufacturing. I did the SeaKlear run and soak overnight, dump, refill, bleach to 20ppm, two hours of cycling, dump again, refill and balance!

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I've been working at this so hard! Now I'm stuck at figuring out how to use the MPS. I'm sure you've gone into more detail elsewhere, but I can't find the term using the "Search" bar.

How much do I add to "help the bleach" work? How much do I add to oxidize what the bleach has already killed? Or am I misunderstanding its role? My tub is 400 gallons. It gets heavy use. MPS doesn't seem to be in the Pool Calculator. Thanks so much.

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If you are using the Dichlor-then-bleach method, then there is no need for MPS. It's the other way around where when using Nature2 with MPS that you need to use chlorine once every week or two to keep the water clear, but when using chlorine you usually only need to use chlorine and do not need to use MPS.

The key to the heavy use is to make sure you dose with enough chlorine after each soak. If you do want to substitute some bleach with MPS to try it, 5 fluid ounces of 6% bleach (3-1/2 fluid ounces of 8.25% bleach) is equivalent to 7 teaspoons of non-chlorine shock (43% MPS).

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OK - I'm new to the chemistry side of hot tubs. We've had the tub for several years now but I just recently started trying to check and balance all of the levels (never had problems in the past but I'm sure water chemistry was not right). I've been posting in the lowering total alkalinity section of this forum but figured this was a better spot to post.

I recently rinsed and refilled tub - balanced all levels. With it still being warm in our area, the tub has only been used once or twice since the refill. We use dichlor for sanitation (vs. bromine). I didn't check the levels again for a little more than a week and the chlorine was almost non-detectable. The pH was also high. All other levels were good. I lowered the pH and "shocked" with the dichlor. I checked today (less than a week later and the pH was high again and chlorine non-detectable. I thought alkalinity was slightly low as well - Taylor book states alk. to be 100-110 and mine was 90 but here it shows lowering to 80. First question - what is the best level for alkalinity? Next - I lowered pH (muriatic acid) and shocked again using the Natural Chemistry concentrated chlorine granules (1 tsp/100 gal.). Question 2 & 3 - why is my pH going up (8) and does the concentrated chlorine go bad with age (shelf-life)? I think this container of dichlor is a few years old. Thanks. I will recheck tonight but my CYA was almost non-existent, pH was 8 but I lowered, alk. like I said was 90 - I did not check hardness but will do so tonight.

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If your pH tends to rise or be too high, then you should lower your TA level. A high TA level causes more carbon dioxide outgassing that raises the pH over time.

The chlorine will not normally last for a week. In a hot spa with no ozonator, the FC typically drops by 25% per day. If you have an ozonator, it could drop by 50% per day or more because ozone and chlorine react with each other. Do you have an ozonator? If not, you could probably add chlorine twice a week if you add a large enough amount. Also realize that you may not be adding enough chlorine to handle your bather load. It takes 3-1/2 teaspoons of Dichlor for every person-hour of soaking so your 1 tsp/100 gal would be good for one person-hour in 350 gallons. The real rule, however, is to add whatever amount of chlorine that is needed so that you measure a small residual 24 hours after your soak. You then need to dose more in between soaks -- you can dose higher to not have to add chlorine every day.

If you have an ozonator, you'll probably not want to use chlorine unless you use the spa every day or two. Bromine is easeier in this case because ozone can create more bromine from a bromide bank and you can have bromine tabs for dosing in between soaks.

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I will check tonight. I was out of town this weekend but do not think my wife got in so there was no use between the last time I checked and adjusted. I'm not sure where or why I figured I needed to add chlorine once per week. I appreciate the assistance. I'm sure I will have more questions later ;-) Thanks again.

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Great info here.  I'm trying to follow it religiously.

One question, what is CD?  In Nitro's post, they say to "Check CD as needed (once a week to start)".  I've searched around and can't figure out what CD is.

Thanks.

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Chlorine Demand.  The percentage of chlorine loss (drop in FC) over a 24-hour period at least one day after any spa usage.  It's the background chlorine loss not associated with bather load.

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So thought i would give this a try, but is it possible to start right now without changing the water? I have around 40 ppm CYA in my tub (Dynasty Spa) and benen using MPS & regular chlorine with CYA.

do i need to lower the CYA more or can i just use more "bleach"? I'm in Sweden and the bleach we have here is weaker than your Clorox bleach.

its in the middle of winter here and the temp is freezing cold! I would really like to wait before changing the water.

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Your CYA level is fine to start by just using bleach.  And yes, if your bleach is weaker you just use more.  However, your bleach may have more lye in it proportionately so may mean you'll need to add more acid to keep the pH in check.

The hardest thing for you will be keeping your pH in check since getting boric acid in Europe is difficult.  If you keep your Total Alkalinity (TA) lower at around 50 ppm then you'll need supplemental pH buffering which is what the boric acid does.  While phosphate buffers are an alternative, if your water is higher in calcium they can precipitate calcium phosphate.

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10 hours ago, chem geek said:

Your CYA level is fine to start by just using bleach.  And yes, if your bleach is weaker you just use more.  However, your bleach may have more lye in it proportionately so may mean you'll need to add more acid to keep the pH in check.

The hardest thing for you will be keeping your pH in check since getting boric acid in Europe is difficult.  If you keep your Total Alkalinity (TA) lower at around 50 ppm then you'll need supplemental pH buffering which is what the boric acid does.  While phosphate buffers are an alternative, if your water is higher in calcium they can precipitate calcium phosphate.

First of all a gigantic thanks to you and all the other members that help us with our spas!!!

Well, I couldn't wait so I have started using our kund of bleach now already :) The water was ok when i started but maybe not crystal clear. I did three treatments with "bleach", I put in so it went up to 5 ppm Chlorine (I'm measuring with the LaMotte ColorQ), and after the third it stayed around 3 ppm for 24 hours and when I opened the cover the morning after the water was all crystal clear!
I had to use 3 dl (10 oz) of our bleach to get to around 5 ppm in my spa (a Dynasty Club7, 350 gallons)

The one comment I've gotten here in Sweden is that it's damaging to the spa to use "bleach" (and that kind of "chlorine") and that it would be damaging to the tubes etc. But i guess I believe you guys more :D

Is the CYA-level needed to protect the spa or why do you need the CYA-level at 30+ ppm? 

 

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Yes, the CYA level of roughly 30-40 ppm (50 ppm is OK but I wouldn't go higher than that) is needed to moderate chlorine's strength.  The active chlorine level is proportional to the FC/CYA ratio though in hot water spas the absolute level is higher than in cooler water.  The reason people say that bleach would be damaging to spas is that if you were to use ONLY bleach with no CYA in the water at all, then the active chlorine (hypochlorous acid) level would be too high and would oxidize equipment more readily.  It would also outgas faster and oxidize the spa cover faster.

At a pH of 7.5, the hypochlorous acid level with 5 ppm FC and 30 ppm CYA at 104ºF (40ºC) is 0.34 ppm.  With 50 ppm CYA it would be 0.22 ppm.  With 30 ppm CYA but at a lower 86ºF (30ºC) it would be 0.14 ppm.  If you had no CYA in the water at all, then it would be 2.2 to 2.4 ppm depending on temperature so over 6 times stronger so would degrade equipment and spa covers 6 times faster.

Don't forget that chlorine slowly oxidizes CYA where in spas it's typically at a rate of around 5 ppm CYA per month so use Dichlor for one day (or so) per month to keep the CYA level up.

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On 2017-03-08 at 6:41 PM, chem geek said:

Yes, the CYA level of roughly 30-40 ppm (50 ppm is OK but I wouldn't go higher than that) is needed to moderate chlorine's strength.  The active chlorine level is proportional to the FC/CYA ratio though in hot water spas the absolute level is higher than in cooler water.  The reason people say that bleach would be damaging to spas is that if you were to use ONLY bleach with no CYA in the water at all, then the active chlorine (hypochlorous acid) level would be too high and would oxidize equipment more readily.  It would also outgas faster and oxidize the spa cover faster.

At a pH of 7.5, the hypochlorous acid level with 5 ppm FC and 30 ppm CYA at 104ºF (40ºC) is 0.34 ppm.  With 50 ppm CYA it would be 0.22 ppm.  With 30 ppm CYA but at a lower 86ºF (30ºC) it would be 0.14 ppm.  If you had no CYA in the water at all, then it would be 2.2 to 2.4 ppm depending on temperature so over 6 times stronger so would degrade equipment and spa covers 6 times faster.

Don't forget that chlorine slowly oxidizes CYA where in spas it's typically at a rate of around 5 ppm CYA per month so use Dichlor for one day (or so) per month to keep the CYA level up.

Thanks again for the answer!

I now have 37 ppm CYA in my spa and it's set to 39 degrees celsius (102 degrees Fahrenheit). So using "bleach" with sodium hypochlorite ("natriumhypoklorit" in swedish) with a 30-50 ppm CYA in the spa isn't more damaging than using ordinary spa chlorine (Dichlor)? 

I use MPS most of the time and then chocking the spa with bleach from time to time. 

I want to continue with bleach, perhaps all of the time, but just want to be certain not to damage the spa!

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On 12/11/2009 at 6:52 PM, Nitro said:

Here is a quick reference to using the Dichlor/Bleach method. (i.e. Chlorine)

Please see the full guide for a detailed explanation. Top link below.

Initial Startup Procedure

1. Balance water by lowering TA to ~80 ppm. See link below (Lowering TA)

2. Aerate until pH is consistently 7.4-7.8. Lower TA if pH rises above 7.8. Raise TA if pH stays below 7.4.

3. Test Calcium, and make note of it. (100-150 ppm) is ok.

4. Add 50ppm Borates (highly recommended)

5. Shock tub to 10 ppm FC using Dichlor the first night after filling.

6. Wait 24 hours and test FC again in order to calculate Chlorine Demand. (See link below)

7. Start using tub.

8. Continue to use Dichlor after soaks (approx 7 ppm FC per person per hour) (or 3.5 tsp)

9. After you have added ~34 ppm FC (~30 ppm CYA) using Dichlor, switch to Clorox 6% unscented bleach. Takes about a week or so.

Ongoing Maintenance

After the initial startup procedure above, you'll basically do the following:

Check FC every day or two (and before soaks).

Check CD as needed (once a week to start).

Add plenty of Chlorine after soaks (and as needed) so FC NEVER drops to zero, and CD stays low.

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

Check pH once a week, and adjust TA as needed.

Rinse filter every week or two, depending on use.

Check CYA every 3 months, and raise by using Dichor if needed. CYA will drop slowly over time.

Use Sea Klear (clarifier) if you experience foam, or cloudy water.

Water Change

After 6 months, change water and start over.

If this is a new tub change water after the first month, then continue bi-yearly.

Consider using a Spa Flush to clean out pipes before draining 1-2 times a year.

Clean filter with TSP every water change.

Lastly, if you let the FC drop to zero for any length of time, the tub is prior owned or you're having serious medical issues (i.e. rashes etc.), consider doing a Decontamination. (see below)

Happy tubbing! :)

I am so sorry, I am so new to this and not very smart when it comes to this.  Some of this I can find on the net.  But what is CD (is CD Chlorine demand)?  If so is that with the yellow tester? What kind of Dichlor do you use?  When you talk about adding chlorine is that bleach?  I don't see any link below, unless I am not reading it right.  What do you mean about after soaks?  what is MPS?  I have a Tuff Spa and pebble tech pool

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I am a new hot tub spa owner and know nothing about the use of chemicals in it -

My hot tub is small and holds 160 gallons of water - it is also equipped with an ozone system -  

How do I care for my hot tub spa on a regular basis?

Thank you for your feedback

Pami W

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4 hours ago, Pami W said:

I am a new hot tub spa owner and know nothing about the use of chemicals in it -

My hot tub is small and holds 160 gallons of water - it is also equipped with an ozone system -  

How do I care for my hot tub spa on a regular basis?

Thank you for your feedback

Pami W

Dichlor/bleach!  Honestly, its been the best and easiest method I've used.  Use the pool calculator to get your chemical amounts right - https://www.poolcalculator.com/.  You input the size of your spa, what you want to do, and it gives you the exact amount to use.

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