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Nitro's Approach To Water Maintaince

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An excellent writeup! Just to note: the 7 ppm FC per person per hour guideline is for a 350 gallon tub. The other way to say it is that the guideline is 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach (e.g. Clorox regular unscented) or 7 teaspoons of MPS non-chlorine shock per person per hour -- that quantity of sanitizer is independent of tub size. This guideline is conservative for fairly hot tubs (near 104F) and as you point out the actual amount depends a lot on the cleanliness of the bathers, how much they sweat, what else they dump into the tub, etc.

 

How many fluid ounces per person per hour for 8.25% Clorox bleach?

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Roughly 3-1/2 fluid ounces of 8.25% bleach per person-hour, but again this is a rough guideline.  You should add enough oxidizer after your soak so that you still measure some (1-2 ppm FC) chlorine residual before your next soak.

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Chem Geek - Thanks for all the great information on this site!  We recently just got our first hot tub and I've been following your dichlor-then-bleach method.  We have a 355 gallon spa set at 101 degrees.  No ozonator.  Have the Taylor k-2006 kit.  Raised the CYA level to approximately 30ppm by measurement of dichlor added.  Typical use is 1-2 adults every 2 days or so with addition of 2 kids (4 total) on weekends.

A few points that I wanted to clarify as well as a few questions - 

1) 1/2 a cup is approximately 4 ounces so using 8.25% bleach - if we have 4 people soaking for 1 total hour, I would need approximately 2 cups of 8.25% bleach to have enough chlorine to oxidize the soak as well as some residual the next day?

2) 50ppm borates (in the form of granular boric acid) according to PoolMath is 14 oz by weight or 15 oz by volume.  So by volume would be approximately 2 cups boric acid.

3) What is the CYA level that you recommend these days?  In the beginning of this thread it looked like 20-30 ppm but I've read a few threads where I think either you or waterbear have recommended slightly higher levels 30-40ppm from years of experience with the dichlor-bleach method.

4) Is there a FC level that would harm the tub?  From my reading of this forum, for those that "shock", they bring FC to approximately 9-10ppm.  I'm planning to be away for 7 days in 2 months and am trying to determine what level of FC I want to raise the spa to prior to leaving.  I've calculated my chlorine demand (though did not do it after initial fill as you suggested - missed a step!) to be approximately 40% at this point in time.

5) What is your recommended routine for filter cleaning/maintenance?  I haven't found much discussion about this issue here.

Thanks again for your time!

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Every person-hour of soaking in a hot (104ºF) tub requires roughly 3-1/2 ounces of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 ounces of non-chlorine shock (43% MPS).  4 people for 1 hour would be 14 fluid ounces or nearly 2 cups BUT you can't soak in 104ºF for an hour so your water temp is likely cooler which means you're not sweating as much so would use less chlorine.  Just experiment since the real rule is to add whatever is necessary such that you still have a small residual of chlorine 24 hours later.

You are correct on the boric acid calculation.

I'd say 30-40 ppm CYA is reasonable.  I was being overly conservative with all the hot tub rash/itch/lung reports from Dichlor-only (and other) users, but the CYA has to get pretty high (100+ and especially 200+) before those reports were more likely to be seen.  That assumes keeping FC in the 1-4 range since one can technically just raise the FC target as the CYA level climbs but most people don't do that.  Also, with higher CYA comes higher FC demand from oxidizing the CYA itself.  So it's best to just manage the CYA level and I think 30-40 ppm is reasonable and 50 ppm is not going to be a problem.

FC by itself is not relevant except from a reserve capacity point of view -- that is, in terms of having enough chlorine to not run out.  In terms of effects on equipment, on skin and hair, on rate of disinfection, etc. it's the active chlorine that matters, mainly hypochlorous acid, and that is proportional to the FC/CYA ratio.  You shouldn't need to "shock" or raise the FC high normally, but as you point out for going away you would.  As for your normal 40% chlorine demand, that won't have chlorine last high enough for a week so you need to turn down your spa's water temperature for when you leave as that will significantly lower the chlorine demand.  The following shows the difference starting at 10 ppm FC and having 40% daily chlorine demand vs. 20% chlorine demand.

Day ....... 40% ...... 20%

.. 0 ......... 10 ......... 10

.. 1 ........... 6 .......... 8

.. 2 ......... 3.6 ........ 6.4

.. 3 ......... 2.2 ........ 5.1 ..... Limit of being OK for 40% demand (if one wants 2+ ppm FC at all times)

.. 4 ......... 1.3 ........ 4.1

.. 5 ......... 0.8 ........ 3.3

.. 6 ......... 0.5 ........ 2.6

.. 7 ......... 0.3 ........ 2.1 ..... Limit of being OK for 20% demand (if one wants 2+ ppm FC at all times)

As for cleaning spa surfaces, other than wiping the main maintenance would be to use Ahh-Some just before you change the water.  If you maintain the spa well you may not need to use it every time but it won't hurt.

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On 2/15/2017 at 11:25 PM, chem geek said:

 

Thank you chem geek for the detailed answers.  Really appreciate you digging into the details.

A few more questions have come up for me as we've been using the tub which has been working great with the dichlor-bleach method.

1) What are you recommendations regarding how and how often to clean the filter?  I have found some information here but methods seem to vary significantly from light spraying to monthly soaking.  I'm thinking regardless, its not a bad idea to buy a second so that when you are cleaning one, the other can be in the tub.

2) How do I know when I need to perform a water change?  The water clarity has been great in the tub though I suspect visual inspections isn't the way to determine.

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How often to clean a filter depends a lot on how much you use the spa and your cleanliness when using the spa.  If you don't use it often or rinse off skin oils and don't use lotions then there won't be a lot getting caught in the filter.  You'll still have your sloughed off dead skin cells.  So this is something you need to judge by seeing how dirty the filter is when you clean it at a certain frequency and also how your water looks since the purpose of filtration is to keep the water clear.

As for a water change, here again it's mostly about water clarity from a buildup of unoxidized organics including those small enough to not coagulate or adhere to the filter.  The other effect of going longer is that there is a salt buildup over time.  Higher salt levels can be more corrosive.  For every 10 ppm FC added by bleach, it also increases sodium chloride salt by about 17 ppm so you can calculate roughly how much you've built up over time.  As for when to change due to salt, you can go to 1000 or 1500 ppm and be fine.  Much more than that increases your corrosion risk though saltwater chlorine generator pools have around 3000 ppm.  The corrosion risk is greater if your spa heater has a copper heat exchanger instead of a more corrosion-resistant cupro-nickel or titanium heat exchanger.  The hotter temperates accelerate corrosion rates and chemical reaction rates in general.

As a rough rule-of-thumb, most Dichlor-then-bleach users are able to go about twice as long as Dichlor-only users and when they do change the water it's not as dull since the change is not as noticeable.  The standard industry Water Replacement Interval (WRI) in days is (1/3) x (Spa Size in Gallons) / (# of bathers per day) though this is probably assuming a roughly 20 minute soak time so the formula is really (1/9) x (Spa Size in Gallons) / (# of person-hours per day).  Doubling that for Dichlor-then-bleach would be (2/9) x (Spa Size in Gallons) / (# of person-hours per day) as a rough rule-of-thumb, but if you are happy with your water and want to go longer and the salt hasn't built up too high, then that's fine.

If you were soaking every day and most of your chlorine usage was from soaking, then if I assume a 350 gallon spa and roughly 7 ppm FC per person-hour in that volume then we have (2/9) x (350) / (1) = 78 days so the salt buildup would be 78*7*17/10 = 928 ppm.  If instead you use the spa only on weekends, then you'd go a lot longer but there would be additional salt built up in between soaks.  Let's say it's 2 person-hours per week, then that's (2/9) x (350) / (2/7) = 272 days.  272*7*(2/7)*17/10 = 925 ppm which (with rounding errors) is the same as before because of the way things cancel out, but we need to add in the salt in between soaks so let's assume 1 ppm FC per day for the 5 days per week so that's an additional 272*1*(5/7)*17/10 = 330 ppm for a total of 1255 ppm.  So still less than 1500 ppm.  This shows that the rough rule-of-thumb of double the standard industry WRI is reasonable, though again you could go longer if you like.

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chem geek and Nitro:  thanks for the information you have shared.  I have checked my chlorine every other day (on a new tub 40 minutes from my primary residence) and have been surprised at how much gets eaten up.  I have been shocking after every use, and so I know this oxidizes chlorine, but a couple times my strips have read 'zero' or close to it.  Has anyone figured out a meter pump dosage rate for feeding in liquid bleach, such that chlorine does not die-off if I need to go a few days without checking it?  By the way, my stabilizer always reads high, so I am switching from dichlor to regular Clorox bleach based on your method.

 

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Hello,

I was wondering if I could get some clarity on nitro's bleach method. I just have a fresh fill on a 500 gal cedar hot tub. The water test looked like this :  CH 100; PH 7.4; TA 90. I brought the CH to 150. I began aeration have added dry acid in stages as needed when ph rises above 7.8. After several additions, a total of 9 ounces the ph still shoots to 8.0 after 30 minutes of aeration. My TA is now around 30. Am I doing anything wrong? Do I still need to keep going?

Thanks for your help!

Michael

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23 minutes ago, ecstatic said:

Hello,

I was wondering if I could get some clarity on nitro's bleach method. I just have a fresh fill on a 500 gal cedar hot tub. The water test looked like this :  CH 100; PH 7.4; TA 90. I brought the CH to 150. I began aeration have added dry acid in stages as needed when ph rises above 7.8. After several additions, a total of 9 ounces the ph still shoots to 8.0 after 30 minutes of aeration. My TA is now around 30. Am I doing anything wrong? Do I still need to keep going?

Thanks for your help!

Michael

I have added a total of 10.5 oz of dry acid and now the ph rise after 30 minutes aeration is down to 7.8. The TA is at 30. I am going to add borates (Gentle Spa) next. Should I boost calcium to improve my csi index? Or any other adjustments?

Thanks,

Michael

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I am now 3 weeks into owning and using my tub. I have been adding in dichlore daily, and using the tub daily. I have been relying on test strips for water balance and sanitation. I bought the Taylor K-2009 drop test kit today and tested and this is where I'm at:

Temp - 100*

PH - 7.6

TA - 130

CH - 290

CYA - 100+

CC - 9 PPG

Should I drain and refill? Or can i shock it with MPS and convert to bleach or is it too late? My CC was higher this AM at 16 ppg after a soak. I added .75oz of dichlor then for a FC of 4.4. Now CC is at 9 ppg and FC 1.2 ppg. I just added .5 oz of Dichlor. what should I do?

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Well, since I couldn't get a response from the forum I went ahead and drained and refilled the tub. Hate to waste all that water. It's a shame nobody is around here anymore to guide us new guys.

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We purchased a new Marquis spa and have had trouble keeping it clear and balanced. Not at first, but gradually I began to really feel affected by the chlorine smell (ours was a bromine system by bull frog) I would get congested and then cough for days after use.  It felt like the chemicals were burning my lungs.  But we also has a foaming film which I now believe to be biofilm, so we are going to decontaminate and sanitize then rebalance. My question is for ongoing maintenance, I wanted to ask if anyone has any experience with IONRX product which is a copper based product used in conjunction with chlorine. The reviews are 5 stars and everyone claims little chlorine fumes and easier to keep clear water. This is recommended by Dr Weil as a less chemical way to maintain clear water.

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