Jump to content
Nitro

Lowering Total Alkalinity

Recommended Posts

"Also, the main cause of pH rise in a tub is outgassing of CO2 from the aeration from the jets and bubblers"

So whe you test you pH, does it matter when you test it? It seems... And I'm only have a short window of knowledge on this, is that right after a 20 min full aeration cycle the pH will be higher that if youlet it "rest" for awhile after the run cycle.

Is this correct?

I dropped my tub last night from 8.0 pH and 150 TA. I could not get much movement in pH,only TA. I let it set over night and its 7.4 -7.6 (drop test) this am and TA looks to be about 40-45 (test strip - didn't have time to drop test it). My FCC was 7.5ppm and this am looked to be 5-6 via test strip.

So, if I run the tub will my pH pick up and then settle down,or just pickup and stay up?

Share this post


Link to post
Share on other sites

Full post of numbers using the Taylor drop tests:

pH=7.5

FC=2.0

CD=.2

TA=60

CH=190

CYA=30-35

Time to switch to bleach. What about my CH?

Using the dropping TA method really got my number more inline. Took sometime and a lot of acid but wow...

Thanks!

Share this post


Link to post
Share on other sites

Your CH is fine. Usually you target 120-150 ppm to avoid foaming, but your 10 is OK since you've got your pH and TA down now.

Aeration raises the pH with no change in TA, but it doesn't "settle back down". However, if the water isn't getting thoroughly mixed, then if you measure near the surface you can measure higher than the average pH of the bulk water. If you are aerating using jets and circulation, this usually isn't a problem. The aeration is driving off carbon dioxide faster and that's also occurring faster at a lower pH which is why the procedure lowers the pH and aerates the water. When you add acid, you lower both pH and TA. So the net result of the process is a lowering of TA.

ACTIVITY .......... pH .... TA ... The following assumes 6.8 is the lowest measurement on the pH test kit

======================

Acid ..................... - ........ - ... Add enough acid to bring pH down to 7.0 (if it's already there, then just skip to the next step, aeration)

Aeration ............. + ....... 0 ... Aerate until pH rises to 7.2

Acid ..................... - ........ - ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)

-------------------------------------

Aeration & Acid .. 0 ....... - ... Continue this combination (cycling of the two above) until TA is at the target you want

then AFTER you have reached your target TA,

Aeration .............. + ....... 0 ... Aerate until the pH rises to your target pH (say, 7.5).

======================

Net of Above ....... 0 ........ -

Share this post


Link to post
Share on other sites

If the pH is rising due to outgassing then the TA is too high so you WANT it to get lower. TA is a SOURCE of rising pH. If you really want to raise the TA back up, then you add baking soda, but that will just keep you in a vicious cycle of acid addition with baking soda addition. To break out of that cycle, let the TA drop lower. For a spa, having a TA of 50 ppm is not unreasonable. For additional pH buffering, you can use 50 ppm Borates (from boric acid; it's what is in Proteam Gentle Spa).

Share this post


Link to post
Share on other sites

Yes, "dry acid" is sodium bisulfate that is commonly sold as "pH Down" or "pH Decreaser" or names like that.

Share this post


Link to post
Share on other sites

Thanks chem geek. I've been a tub owner for 2 years, and haven't paid a lot of attention to chemistry... fortunately, the tub has remained pretty nicely clean with the dosage of dichlor I've always given after each use (just my wife and I). However, coming across these threads makes me think I've been VERY lucky. I have the Taylor on order, and intend to get a strict regimen going when it gets here.

Share this post


Link to post
Share on other sites

Okay... Need some clarification.

Your example is 300ppm and pH greater than 7.8. You calculated 19oz... How? The pool calculator won't tell you this.

Anyway, I have a 340 gallon fresh fill. I thought I would balance it first this time.

My TA was 200 and my pH was 7.2.

I calculated incorrectly and started with 7.6 oz (I did a ratio of 300 over 240 = 19 over X and got 15.2). Ran full jets, air, etc and it dropped to TA of 130 and pH went to 7.8.

According to the chart at the top, I need to go to step 2 and recalculate my amount needed. You example shows you going from 1 cup to 6oz to 3, then 2 then 1 even though your pH is greater than 7.8.

I recalculated and came up with adding 4.12 oz (half of 8.23) and did it again. This time I got a TA of 125 and pH of 7.8. So in this scenario I would got to step 2 and recalculate. This time I would use 2.57 oz (half of 5.145).

Is this last step correct assuming 100 over amount to reduce = 8 over "X"

100,,,,,,8

----- = ----

65,,,,,,,X

Thanks... I have not added dichlor yet... So it straight town water.

Starting numbers from the tap.

PH 7.2

FC 1.2

TA 200

CH 240

Share this post


Link to post
Share on other sites

If you scroll down to the "Effects of adding chemicals" section in The Pool Calculator you will see how much adding acid lowers the TA. For your 340 gallon spa (entered after "Size" at the top of the page), 117 ounces of dry acid lowers the TA by 1001 ppm so 1.17 ounces weight (0.78 ounces volume or 4.7 teaspoons) lowers it by 10 ppm (I use scaled up values to get more decimal places -- otherwise, you see that 1.17 to 1.22 all say 10 ppm). The amount of TA drop from acid is independent of pH.

If you do the calculation using 350 gallons and 240 ppm TA from Nitro's write-up, you get 29 ounces weight which is about 19 ounces volume (you can see that ratio in the "pH" section for dry acid).

In 340 gallons, your TA drop of 70 ppm implies 7 ounces weight or 4.7 ounces volume of dry acid. Was your 7.6 ounces weight or volume?

Don't overthink the procedure. It cuts in half for each step just to reduce the possibility of going too low in pH for too long. So you don't need to worry about your initial amount. Just see how much TA you have left to go and add half the required acid amount.

Share this post


Link to post
Share on other sites

I was doing weight... Is that correct?

I see in the calculator that 7oz in 340 reduces TA by 60. Is the 7oz by weight?

My number tonight after tweaking are TA50 and PH 7.6, ran another 20 minutes (1cycle, no adjustment) and TA 50 and PH 7.8. (Sunday)

My FC is 7.6 today, 24 hours after dosing it with Dichlor to 10ppm. (Monday)

It was a new tub,one month old, so we dumped the water even though it was crystal clear. We used SeaKlear first and wow... What a scum line. Not horrible, just unexpected. Will be doing the bleach / dichlor method again.

I don't dare go lower than TA of 50 do I?

Side note... How much Gentle Spa do I add to get to 50ppm in a 340 gallon tub? I get 13oz but thats using Boric Acid as the chem. from the App.

(Tuesday)?Didn't add Gentle Spa yet, waiting on confirmation for amount. But tonight's numbers are TA 50 PH 7.6 and FC 5.2.

Tub has has no use since I filled it. I want to balance it first. Is it okay to add the Gentle Spa now. I'm not sure if I'm balanced or not.

Thanks....

Share this post


Link to post
Share on other sites

Yes, that was correct. Your 7.6 ounces is close to the 7 ounces weight that was expected. The Pool Calculator "Effects of adding chemicals" uses weight. The only place you see volume is in the upper sections where it shows both saying things like "# by weight or # by volume of dry acid".

50 ppm TA should be good. The instructions for ProTeam Gentle Spa say 4 ounces (weight) per 150 gallons so for your 340 gallon tub that's 9.1 ounces weight. They may not be going up to 50 ppm -- they are probably going to around 30-40 ppm. I'd just use 13 ounces since they say one can add 2 ounces per 150 gallons in between drain/refill cycles so that's a total of 6 per 150 gallons or 13.6 ounces for 340 gallon.

You can add the Proteam Gentle Spa now since you've got a good water balance. Some people report the pH rising right after adding this product so you might have to add some acid to lower it. With pure boric acid, that won't happen and it's instead slightly acidic.

Share this post


Link to post
Share on other sites

I went with 12oz (2-6oz packs). I'm not clear on how you got to 13 oz with the 2oz every 150 gallons. I would get closer to 10 and that would seem like it would give you 60ppm. I hope I'm wrong in my math because using boric acid it tells me 13oz.

I was 7.5,pH and 50ta. I'll report after my tub cycles for a bit what it jumps to.

After Gentle Spa:

TA 70. pH 8.0+

I dialed it down to 50TA and pH settled in at 7.8 for 2 cycles. If I don't get in I bet it would be 7.6 in a while. But, we're gonna hop in and enjoy our tub.

Let me know if something seems off with what I did...

Thanks -

Scott

Share this post


Link to post
Share on other sites

50 ppm borates in 340 gallons is 13 ounces weight (14 ounces volume) of boric acid. The Gentle Spa recommended initial amount is probably not for 50 ppm borates. Anyway, what you've got is fine.

Share this post


Link to post
Share on other sites

First off, I would have used bleach instead of Dichlor so that you wouldn't be increasing your CYA level. For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm. As the CYA gets higher, then for the same FC level the active chlorine level is lower so disinfection and oxidation rates go down. For simplicity, think of the active chlorine level being proportional to the FC/CYA ratio.

Breakpoint chlorination is wrong if you are talking about the 10x rule. The rule came from the breakpoint chlorination of ammonia by chlorine, NOT of Combined Chlorine (CC) by chlorine. Ammonia is measured in ppm N (Nitrogen) units while chlorine and combined chlorine are measured in ppm Cl2 (molecular chlorine) units and there is roughly a factor of 5 difference between these. The oxidation formula has 3 chlorine for every 2 ammonia, so a ratio of 1.5 to 1 so multiplying by the factor of 5 one gets 7.6 (using the exact numbers) and due to side reactions and needing to get over the hump of the first reactions, in practice it's 8-10x from which the "10x rule" was born. Problem is, that combined chlorine is already in chlorine units so that's a factor of 5. Combined chlorine also already has 1 of the 1.5 chlorine needed. So in terms of chlorine demand, and accounting for organic combined chlorine and not just inorganic combined chlorine, the rule is no more than 3x. Even then, using more just makes things go faster and using too little just means you can add more later as nothing gets "stuck".

OK, back to what you saw. I suspect you had ammonia (originally; now monochloramine) or organic precursors (such as urea or creatinine) in your water. Had you left your initial water alone, the FC would have dropped and the CC might have gone up but for CC it depends on what type. Anyway, you had something in the water that consumed FC. So the FC you added partly oxidized some of the CC, but it also reacted with precursors to form more CC that was then oxidized. What you need to do is to keep shocking with chlorine until your 24 hour chlorine loss rate is around 25% if the water is fairly new and you don't have an ozonator (with an ozonator or with older water the loss rate may be 50% or more).

Now part of the problem is that your CYA is high. As I mentioned, this slows down chlorine reactions because most of the chlorine is bound to CYA. So it's easier for your spa to "get behind" from bather load because the chlorine isn't able to oxidize it fast enough due to the high CYA level. So if you use your spa regularly, then you are continuing to add chemicals to the spa that need to get oxidized, but the active chlorine level is too low so such chemicals build up as does CC. This is why we recommend the Dichlor-then-bleach method since after an initial 30-40 ppm or so of CYA, the subsequent bleach prevents the CYA from rising. You add Dichlor about once a month to make up for a slow loss of CYA, but basically you keep it fairly constant so that the active chlorine level remains fairly constant. Also, you make sure you add enough chlorine after each soak to handle all the bather waste; many people simply don't add enough. We have rules-of-thumb for how much to add, but you really just add whatever is needed so that you measure at least 1-2 ppm FC for the start of your next soak (or 2-4 ppm FC 24 hours after adding the chlorine, if you don't soak every day; you then need to add more chlorine in between soaks to maintain its level though can let it drop to 1-2 ppm FC just before your next soak).

Share this post


Link to post
Share on other sites

Yes, since your CYA is already up, use sodium hypochlorite (chlorinating liquid or bleach) to raise the FC up.

As for routine maintenance, you need to MAINTAIN a disinfectant level in your spa at all times and unfortunately chlorine won't last more than a few days. So you'd have to add it every day or two or if you raised it to a higher level then perhaps once or twice a week (though such raising will be harder on the hot tub cover). The chlorine system is not designed for spas that are not used every day or two or at least twice a week. If you want to use chlorine, then you should look at getting the http://www.controlomatic.com/technichlor.html'>ControlOMatic TechniChlor saltwater chlorine generator so you can have it generate a background level of chlorine between uses. Some spas have their warranty voided if you raise the salt level to the 1500-2000 ppm needed by this generator.

Otherwise, people who use a spa infrequently will often use bromine instead of chlorine because with bromine you can use bromine tabs that slowly dissolve and should last about a week or sometimes two (depending on how many tabs you put into the feeder). However, bromine and its bromamine by-products smells different than chlorine and some people don't like it.

Share this post


Link to post
Share on other sites

If you want to convert to bromine, you can do so without changing the water. It's converting from bromine to chlorine that requires a water change. To convert from chlorine to bromine, you just add sodium bromide and start using bromine tabs. Since you don't know if you would like bromine, perhaps you can try it in the spring so if you don't like it you can go back to chlorine with a water change.

Share this post


Link to post
Share on other sites

It is not true that unstabilized chlorine in household bleach will not last long once diluted in the tub water because you already have CYA in the water that stabilizes it. If you were referring to bleach going bad when concentrated, that does happen but it's usually not very fast for quality bleach. It's more concentrated chlorinating liquid that degrades about 4 times faster. Of course, any concentrated sodium hypochlorite chlorine left in hot temperatures will degrade faster.

The only way to lower the CYA level is through water dilution. It does degrade slowly over time, but around 5 ppm CYA per month at hot spa temperatures so not very fast.

Share this post


Link to post
Share on other sites

If you had no CYA in the spa water at all, then adding unstabilized chlorine will outgas faster, that is true. And of course if it's exposed to sunlight it will break down rather quickly losing around half every hour. This is why it's the "Dichlor-then-bleach" method and not the "bleach only" method. The CYA is needed to reduce the active chlorine level which reduces the rate of loss from outgassing and reduces its strength of oxidizing skin, swimsuits and hair as well as harshness on equipment and covers.

Oh, 2 years old is quite old. I didn't realize that it was so old. 6% bleach can last for many months, even a year if kept out of hot temps, but 2 years is most definitely pushing it. The table at the bottom of http://www.odysseymanufacturing.com/about_product.htm'>this post will give you some idea of how quickly various concentrations of bleach or chlorinating liquid lose half their strength at various temperatures.

The high CYA level lowers the active chlorine level so this means with the usual FC levels the chlorine reacts more slowly. With a higher bather load you could get behind in trying to oxidize bather waste. If you only soak once or twice a week, you might be OK, but if you soak every day or two you could find that the chlorine is not able to keep up and eventually your water may turn dull/cloudy. The disinfection rate is also lower, though most bacteria are easy to kill. With very high CYA, somewhere well above 100 ppm, there seems to be more likelihood for getting hot tub rash/itch from Pseudomonas aeruginosa. So you can just chance it since perhaps your CYA isn't much over 100 ppm. Up to you. This will certainly get fixed on your next water change or you can do a partial drain/refill if you don't want a complete one.

Share this post


Link to post
Share on other sites

Yes, it would be better to use bleach now since your CYA is already high. Don't use any more Dichlor until your next water change.

Share this post


Link to post
Share on other sites

Your mind isn't feeble. You're doing great!

Share this post


Link to post
Share on other sites

I posted this earlier under my old forum name and somehow got black listed so I'm back, asking 2 questions;

For the admin;

1 - why was I banned from this forum? I reported some responses to this thread as spam and then I'm out? I've sent the admin multiple emails asking this question and have yet to receive a response. If it turns out that the spam cam from me I would like to know because then it would mean that my computer has been compromised and I would get it cleaned...

For anyone else;

2 - my original question - when I add Dichlor to my hot tub - I like to have it predissolved - thinking this helps it circulate and become homogenous. Everything (OK almost everything) dissolves a lot faster in hot water. So I add the granules to water that I get from a hot water dispenser on my sink (160-180F). Will this hot water cause the dichlor to degrade or cause problems?

Lastly for the admins; If you access this site by searching “pool and spa forums” in Google Chrome using McAfee Antivirus, your site shows up as being unsafe. Apparently your SiteLockSecure program isn’t playing well with McAfee. Remember this is coming from someone that has been blacklisted from your site for some reason. I have a screen shot if anyone cares to see it...

Share this post


Link to post
Share on other sites

The Dichlor in hot water will be OK for a short time. It would be an issue over days, mostly in increased chlorine outgassing and increased rate of oxidation of CYA by chlorine (so yes, that can be considered to be breakdown of the Dichlor). Are you sure your hot water tap is 160-180ºF? Even at 140ºF it only takes 3 seconds for a 2nd degree burn and 5 seconds for a 3rd degree burn.

Share this post


Link to post
Share on other sites

Well - I'm not using the hot water any more - going to try without it since each week the chlorine level is almost at zero. And to answer your question; it is not my hot water tap. It is a hot water dispenser for making tea, instant coffee, oatmeal... It is safegarded in as much the lever is on the back side where it can't be inadvertently activated. It is mounted on the back of thie sink. I checked it after you asked since I knew it was up there but had no idea how hot. I used a non contact IR thermometer and it is 183 F. So yes - it could burn quickly.

Share this post


Link to post
Share on other sites

Yes, that was correct. Your 7.6 ounces is close to the 7 ounces weight that was expected. The Pool Calculator "Effects of adding chemicals" uses weight. The only place you see volume is in the upper sections where it shows both saying things like "# by weight or # by volume of dry acid".50 ppm TA should be good. The instructions for ProTeam Gentle Spa say 4 ounces (weight) per 150 gallons so for your 340 gallon tub that's 9.1 ounces weight. They may not be going up to 50 ppm -- they are probably going to around 30-40 ppm. I'd just use 13 ounces since they say one can add 2 ounces per 150 gallons in between drain/refill cycles so that's a total of 6 per 150 gallons or 13.6 ounces for 340 gallon.You can add the Proteam Gentle Spa now since you've got a good water balance. Some people report the pH rising right after adding this product so you might have to add some acid to lower it. With pure boric acid, that won't happen and it's instead slightly acidic.

Being that we now know Pro Team Gentle Spa raises the pH - would it not be wise to just add the gentle spa at the beginning of the process and lowering the pH with dry acid all at one time or is it not that simple? Will It through other numbers off?

Share this post


Link to post
Share on other sites

It's harder to move the pH once the borates are added, so I would just keep the pH low and aerate the water while adding acid to lower the TA, but then instead of raising the pH once the TA is reached, then use the ProTeam Gentle Spa to add the borates. If the pH still overshoots, just add some acid to compensate.

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...