Time For New Water?

[freeradical]

Hello,

I've had 500g spa since mid Feb '10 using Nature2 + MPS + dichlor shock prn. Follow Nature2 directions w/MPS testing prior to tub use + 1 oz/person-hour use time on exiting. Have had some skin changes (but no other spa user has had this) which may or may not be related to the spa, so I decided to shock w/ dichlor. CYA previously tested approx. 70 by visual cloudiness test. Poolcalculator.com recommended 2 oz dichlor in order to shock to 20 ppm given CYA level. FC was 33 ppm 30 min after adding dichlor + circulation. 24h later, level dropped to 1.4 by FAS-DPD test. Pool store then tested water w/ FC @ 0.5 ppm and CYA at 41 ppm by pinpoint analysis system. Should I keep adding dichlor until I get a more normal FC degradation time (in case there is something in the water that should not be there)? Or, maybe I should just wash the filters, clean the spa and refill it. I am due for 4mo recommended water change in mid June. Thanks for your help.

[polyvue]

Hello,

I've had 500g spa since mid Feb '10 using Nature2 + MPS + dichlor shock prn. Follow Nature2 directions w/MPS testing prior to tub use + 1 oz/person-hour use time on exiting. Have had some skin changes (but no other spa user has had this) which may or may not be related to the spa, so I decided to shock w/ dichlor. CYA previously tested approx. 70 by visual cloudiness test. Poolcalculator.com recommended 2 oz dichlor in order to shock to 20 ppm given CYA level. FC was 33 ppm 30 min after adding dichlor + circulation. 24h later, level dropped to 1.4 by FAS-DPD test. Pool store then tested water w/ FC @ 0.5 ppm and CYA at 41 ppm by pinpoint analysis system. Should I keep adding dichlor until I get a more normal FC degradation time (in case there is something in the water that should not be there)? Or, maybe I should just wash the filters, clean the spa and refill it. I am due for 4mo recommended water change in mid June. Thanks for your help.

If this was my spa and I was able to document a 30 PPM chlorine drop in 24 hours I would drain, clean the filters, decontaminate and refill.

[chem geek]

Also, do not use Dichlor for shocking unless you intentionally want to increase your CYA level. You would normally use bleach for shocking instead.

For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm.

[freeradical]

Also, do not use Dichlor for shocking unless you intentionally want to increase your CYA level. You would normally use bleach for shocking instead.

For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm.

I used dichlor because I will be changing the water soon anyway and was not too concerned with having it rise too fast. I have heard mixed things about bleach. I have read yours and Nitro's info re: dichlor then bleach method which makes good sense to me. I have had some people at the local dealer tell me to use bleach initially to activate the nature2 cartridge. I have had others say never use any bleach because it is "too strong." My owner's manual says never to use any nonstabilized liquid chlorine product and that it would affect the warranty coverage for the spa. The manufacturer's customer rep says never to use any bleach (she did not know what sodium hypochlorite was) because it is not strong enough- actually said because it is 6% concentration that I would have to use "6 gallons" to get the FC to the proper level! I am so tired of the misinformation and misguidance in this industry. Would love to talk to someone directly in my area that actually understands the chemistry behind the methods (as you do) as I have a science background.

[polyvue]

Also, do not use Dichlor for shocking unless you intentionally want to increase your CYA level. You would normally use bleach for shocking instead.

For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm.

I used dichlor because I will be changing the water soon anyway and was not too concerned with having it rise too fast. I have heard mixed things about bleach. I have read yours and Nitro's info re: dichlor then bleach method which makes good sense to me. I have had some people at the local dealer tell me to use bleach initially to activate the nature2 cartridge. I have had others say never use any bleach because it is "too strong." My owner's manual says never to use any nonstabilized liquid chlorine product and that it would affect the warranty coverage for the spa. The manufacturer's customer rep says never to use any bleach (she did not know what sodium hypochlorite was) because it is not strong enough- actually said because it is 6% concentration that I would have to use "6 gallons" to get the FC to the proper level! I am so tired of the misinformation and misguidance in this industry. Would love to talk to someone directly in my area that actually understands the chemistry behind the methods (as you do) as I have a science background.

SIX gallons?! In a spa? Invite that customer rep over to sit in that concentration for a while!

[NewB@Spa]

Well I can certainly chime in here. I have a 400 gallon spa that I have owned (brand new) for approximately 7 months. My first fill went horribly mostly due to bad/misinformation from dealer and spa "experts". I was fortunate enough to happen upon this site and Nitro and Chem Geek's suggestions have been instrumental in my renewed enjoyment of my "baby". I filled nearly four months ago (due for a re-fill soon). After balancing initially with Calcium Chloride (~150) I get my TA in line (~80 to start). Typically that same day once everything is balanced I add the Borates to 50ppm - all of this is done with the indispensable assistance of the Pool Calculator. Usually the next day I start my course of Dichlor (to build CYO), this step the last time took approximately 5 days until I had a CYA of 30ppm. To make things easier on myself I did not use the tub throughput this entire 5-6 day process. I then switched to 6% Chlorox regular bleach and have been a happy camper ever since.

I calculate my bleach use over the last 3 1/2+ months as approximately 1 gallon (~$2.00) versus lord knows how much Dichlor and multiple other chems that the "experts" recommend. They recommend it so they can sell you on a program of chems that keeps you coming back. Bleach is all you need for your day-to-day sanitation. After a typical 1 or 2 person soak (20-30 minutes) I throw in about 1/2 C of bleach which keeps my FC at about 5-6ppm, certainly not 6 gallons! My PH has never varied from between 7.2 and 7.6 - I have only used MPS once in nearly 4 months, but maybe mine doesn't get amount of usage as some.

[freeradical]

Well, I have emptied and decontaminated the spa using nitro's decontamination procedure in combination with the decontamination procedure from Hot Springs. Refilled the spa yesterday with filtered water and balanced the water:

pH 7.6 (after adding 1.25 dry acid to correct a pH > or = to 8.0); interestingly, pool store "pinpoint analysis" meter measured 7.6 and they rec. 1/2 oz acid which did not budge the pH

TA 70

TH 140-150 (pool store said 183- >20% difference)

Added Nature2 cartridge and shocked with dichlor as recommended by nature2 instructions (1.5 Tbls/250gallons)= used 3 Tbls (1.5 oz) since I have 500 g spa.

Tried to check FC 30 min later, but ran out of titrating agent. Should have been ~13 by pool calculator.

This afternoon, I added 20 oz Proteam Gentle Spa (~48-49 ppm borates) around 4 pm.

At 6:30 pm (23.5 hours after superchlorinating and 2.5 hours after adding borates),

T= 97.8

pH > or = 8.0 with acid demand of 4 by Taylor test kit (requiring 2.47 oz 93.2% Na Bisulfate to correct to pH 7.6)

FC 14 (perhaps I added 3 oz dichlor? I doubt this.)

CC 0.5 (why not 0?)

TA now up to 90

Will recheck FC in 24 hours to determine chlorine demand. Any additional suggestions for pH management, etc?

I would like to confirm that I added the correct amount of Gentle Spa as well: Using the following post by chemgeek as a guide, I added 20 oz by volume to get to 48 ppm by the pool calculator selecting boric acid in the drop down selection box. By bottle directions, would add 13.3 oz (500 g pool), but bottle doesn't state the ppm this would yield. The MSDS for the Gentle Spa product only lists Sodium tetraborate pentahydrate as an ingredient + "proprietary ingredients." If this ingredient selected using pool calculator, 12 oz calculated to reach 50 ppm borates.

http://www.poolspaforum.com/forum/index.php?showtopic=24321&st=0&p=104706&hl=gentle%20spa&fromsearch=1entry104706

"QUOTE (DubyaB @ Mar 28 2010, 07:56 PM) <{POST_SNAPBACK}>

Ya I had the borates in. Not totally sure though at what level. I put 2 cups of Borax in at the water change but not positive on what ppm that would have given me in 360 gallons.

2 cups of boric acid (Proteam Gentle Spa) in 360 gallons would be 52 ppm borates so right on the money! If you used 20 Mule Team Borax instead (with associated Muriatic Acid), then that would have been 39 ppm borates. The Pool Calculator will give you dosages and near the bottom the "Effects of adding chemicals". Just make sure you enter in your spa volume properly near the top. "

[freeradical]

Recheck 9:45 am today:

T97.1, pH ≥ 8.0 w/ acid demand stable at 4 drops to reach pH 7.6, TA 90, FC 11.0, CC 0.5

BTW, I have an ozonator. Had 3 ppm drop / 15 hours. This extrapolates to ~ 5 ppm over 24 hours, if degradation curve linear, yielding a chlorine demand of approximately 35% [1-(9/14)].

At this point, should I just go ahead and add the acid required as calculated by the acid demand test?

[polyvue]

Recheck 9:45 am today:

T97.1, pH ≥ 8.0 w/ acid demand stable at 4 drops to reach pH 7.6, TA 90, FC 11.0, CC 0.5

BTW, I have an ozonator. Had 3 ppm drop / 15 hours. This extrapolates to ~ 5 ppm over 24 hours, if degradation curve linear, yielding a chlorine demand of approximately 35% [1-(9/14)].

At this point, should I just go ahead and add the acid required as calculated by the acid demand test?

pH control is crucial and the TA may be a little high... I didn't run the numbers, but you can using the Pool Calculator. You've got a lot going on here in the two days since it was filled. I'd recommend continuing to add small amounts* of acid to reduce pH and TA, testing between applications. Chlorine demand is a different matter. As I don't have hands-on experience managing a spa that incorporates so many different methods of sanitizing (ozonator with "Nature2 + MPS + dichlor shock prn") and uses borates.... I hope others will offer their advice.

Using a 10 mL sample for the FAS/DPS chlorine test? If so, don't worry about a Combined Chlorine (CC) total of .5 PPM. You can always increase the sample size to 25 mL (each drop of reagent R-0871 = .2 PPM) to get a bit more resolution. If CC tests > .5 PPM with either 10 or 25 mL I'd suspect MPS interference. More on this at http://www.poolspafo...showtopic=22984

Are you testing for Calcium Hardness (CH) and cyanuric acid (CYA)? I didn't see those numbers. If you run Pool Calculator, be sure the CYA and CH values are entered.

* Free Chlorine may be high enough to have a slight affect on the pH test result; this combined with test imprecision (due to imperfect ambient or back light when color matching pH level, variability in size of sample, titrant drops) would lead me to be cautious when making adjustments. If the spa jets have been working overtime, as I assume they would be while you're adding chems, mixing, testing and adjusting, the resultant aeration will tend to increase pH.

[freeradical]

Hi Polyvue. I listed calcium hardness as "TH" above for total hardness level which is around 140-150. Using acid demand test requirements as an endpoint, added 1 oz sodium bisulfate in two doses. Last readings 27 hours after the free chlorine level of 14 follow:

pH 7.6

TA 70

FC 8.8 (avg of 8.5 and 9)

CC 0-0.5

Borates 48 (if calculated correctly)

CSI -0.13

I did use the 10 mL sample. Also, I have neither added MPS nor used the spa since refilling. Looks like everything is stabilizing. Will consider slight adjustment of TA to 90. Should be ready to use today. Chlorine demand ≅ 37% over 24 hours.

Thanks.

[chem geek]

Just so you know -- an ozonator is both good and bad with respect to chlorine demand. It will actually consume more chlorine when you are not using the tub (mostly oxidizing chlorine to chlorate, but may also be forcing more outgassing of chlorine) and is probably why you are seeing a 37% chlorine demand instead of the more usual 25% after a fresh refill in spas without an ozonator. The plus side is that when you are using the tub, the ozonator will oxidize some of the bather waste lowering the chlorine demand for doing so. This means that an ozonator is usually worth it if you use the tub frequently, say every day or two, but may not be if you don't use it very much, say once a week -- at least as far as chlorine demand is concerned.

The ProTeam Gentle Spa is mostly boric acid with a little sodium tetraborate pentahydrate added for a more neutral pH (boric acid alone is slightly acidic). Using the Boric Acid in The Pool Calculator is the right thing to do and will be pretty darn close to accurate for this product.

I believe the main reason there is so much confusion about using bleach (other than the financial disincentives since that's not what spa dealers sell) is that using ONLY bleach in a spa would be too harsh since the active chlorine level would be too high (at 104ºF, 4 ppm FC with no CYA has more than 6 times as much active chlorine as 4 ppm FC with 30 ppm CYA). Cyanuric Acid (CYA) significantly reduces the active chlorine level. This is known science since at least 1974 when the equilibrium constants between hypochlorous acid, CYA and the chlorinated isocyanurates where definitively determined. You can see this definitive scientific paper here and can see the spreadsheet I used to calculate various water parameters here though that is not for novice users (The Pool Calculator is easier to use, but does not calculate as many items, including actual hypochlorous acid level). Note that I have the temperature dependence of the Cl-CYA equations turned off by default -- for a spa you might want to turn those on at line 225 (both columns B and C should be set to "TRUE"). I have that off by default since I'm not confident of the temperature dependent equilibrium constants (i.e. the activation energy) as it came only from one source (Wojtowicz) and not from a peer-reviewed study or from more than one researcher.

[freeradical]

Chem geek,

Thank you for the information. Couple of questions: can the pool stores equipment accuracy vary to the degree it did with my home readings if they do not perform proper calibration? Also, do you happen to have a graph of a free chlorine degradation curve for your own or another pool? I am curious about how a "typical" spa free chlorine degradation graph would look. It would be zero order, correct?

[freeradical]

Today's first values:

T 97

pH 7.7

FC 3

TA 70

CH 140

Tried to adjust pH down. TA inc. to 100 w/ baking soda. (Yes, I knew this would inc. pH but was erroneously thinking I needed to compensate for buffer loss incurred when adding dry acid.) Added dry acid to drop pH to ~7.2 while aerating spa. Let continue to aerate for 30 - 45 min and rechecked:

T 104

pH 7.7

TA 50

FC 2

CC < or = 0.5

CH 140

Right back where I started except loss of TA. BTW have ozonator and added borates to 48 ppm last week.

Added 3 tsp (0.5 oz) to increase FC from 2 to 6 and 30 min later, FC=10? Used pool calculator to determine value. Why the big increase? Did I check too soon?

Also, do I need to go ahead and adjust CH to higher level (~200) or should I see if values stabilize first?

Thanks again.

[chem geek]

Pool stores are notorious for doing inaccurate testing, especially with the CYA test. Many pool store employees are seasonal so are often new and not trained very well. You should trust your numbers.

The drop in Free Chlorine (FC) over time is mostly an exponential decay curve (1st order decay) since most chlorine degradation processes are proportional to its concentration. So a certain percentage of chlorine degrades from sunlight, some gets used up oxidizing bather waste (though this is not all first order), some gets used up oxidizing CYA, and some gets used up oxidizing other organics and materials found in the pool or spa. There are some chemical reactions that are so fast that they have the chlorine drop appear to be more like zero order. Part of bather waste is like that since chlorine combines with ammonia to form monochloramine very quickly, but then more slowly oxidizes this to nitrogen gas. Urea also takes longer to oxidize though in spas it is usually complete within 24 hours while in pools it takes days (though UV from sunlight may help accelerate this -- not sure).

In practice, in a spa the bather waste appears to be zero order chlorine drop because it mostly gets oxidized within 24 hours. Other sources of degradation are more like first order exponential decay as they are slower so can be measured in 24 hours. That's why a chlorine demand test with no bather load is so useful since it gives you an idea for this first order decay -- the percentage of FC lost each day. The ozone oxidation of chlorine would probably follow first order as well since the reaction rate depends on both the ozone concentration (which is fixed) and the chlorine concentration (which varies over time).

Generally speaking, hot spas start out with a chlorine demand of around 25% (with no bather load) if they have no ozonator while those with an ozonator may lose 30-50% depending on the strength of the ozonator and how long it runs. The chlorine drop in pools not exposed to sunlight is fairly low at around 10-15% per day depending on temperature. Pools exposed to sunlight typically lose around 15-50% per day depending on the amount of sunlight and the CYA level -- at high CYA levels near 100 ppm the losses are done to around 15% per day while at 30-40 ppm CYA they can be closer to 50% in areas with a lot of sunlight. If there were no CYA, then such pools would lose nearly 50% per hour near noontime.

[chem geek]

I would wait to stabilize your pH and other values before adjusting the CH. As for the larger increase in FC, perhaps it wasn't thoroughly mixed or there was measurement error or the product is denser than we assume -- it sounds like you are using Dichlor since this is after a fresh refill and you are building up CYA.

Don't try and raise the TA. Leave it at 50 ppm. It won't go down unless you add acid. As you found out, adding acid and aerating is a fast way to lower the TA. The acid is what lowers the TA, but since acid also lowers pH the aeration raises the pH letting you essentially drop the TA without changing the pH.

Again, see what happens to the pH when the TA is at 50 ppm. Don't try and lower the pH below 7.5 at this point. It might slow down in its rise near 7.7.

[freeradical]

Thanks for the info, Chemgeek. I'll just keeping checking the pH / TA for a while.

[3ginfomanagement]

Hello,

This thread is very informative.

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[freeradical]

ChemGeek,

Today's values follow.

T 96.9

pH 7.5 (has been 7.5/7.6 since last post)

TA 50 (no change since last post)

Total Hardness 140

FC 3.0

CC 0

CYA ~ 25.7 ppm (based on 3.19 oz dichlor added thus far since water replacement); no Na Hypochlorite used yet.

CSI currently about -0.47 by pool calculator. Time for more calcium chloride to improve CSI?

Thanks for your input.