total alkalinity vs ph -- questions from horticulture background

[mrwoo]

Greetings. I found this site and am very excited because it's got a lot of answers to my questions.

First, I am about to receive my first hot tub of my own, a bullfrog. So I am investigating the maintenance aspects of the water quality.

I am wondering though if someone could explain something to me concerning the pH? I know what pH is. My job is to maintain a water quality level for plants in a large retail greenhouse. I used to monitor pH (ours is 7.6 to 8.1 depending on aquifer levels from runoff) and then add H2SO4 to bring it down to about 5.8. However as I learned more about the pH levels needed for maximum nutrient uptake, I stopped looking at the pH because it was only an indicator of the alkalinity.

I test the EC of my water (0.25ms) then add fertilizer (salts = conductivity) and measure EC again to know my PPM of the solution (which is then diluted with chemical injectors). I also test the alkalinity of my water for CaCO3 (typically 125 ppm CaCO3) and then chemically inject H2SO4 to neutralize the alkalinity down to about 70ppm. This naturally brings the pH down with it although it may not be exactly at 5.8, it could be higher or lower. But the caveat here is that it is the CaCO3 levels that matter. The pH of the solution has such a very small power to indicate the alkalinity.

So my question here is, for those who may know what I am talking about, shouldn't one just titrate the alkalinity, and use a chemical to bring it to the optimum level and not worry about pH? This assumes your water is very very clean from heavy metals etc and that only has a high or low alkalinity level. pH being the potential of H in the solution will be lowered when the CaCO3 is broken apart and the free H increases. This is coming from using H2SO4 which very easily free's the extra H from the CaCO3.

I know I am missing something here relating to hot tub chemistry. I understand chlorination and sanitizing as I do well shocks when we change pumps and I use chlorine dioxide to disinfect biofilms in plumbing etc. What I'm seeking to understand is how the pH itself has such importance on so many hot tub "how to's" when pH itself going up or down is not really what is happening or described properly but that what is IN the water that is chemically happening is really what's going on. So in my mind, if my water starts at 180 ppm of CaCO3, and I use a Hach Digital Titrator to monitor it, and use whatever chemical to lower it to a hot tub's optimum, would the pH measurement still be such a critical piece of data?

Thanks for anyone who might care to share. I like technical explanations and I don't mind being told I am wrong. It's about learning for me.

 

[JoyfulNoise]

As you alluded to, but worth reiterating, pools & spas are NOT horticultural water bodies, so you have to be careful when mixing and applying principles from one to another.

First, some clarification - there is NO hydrogen in CaCO3. And, as far as "alkalinity goes" it is Total Alkalinity (TA) and the results are reported in units of CaCO3 but TA is a mixture of ALL alkaline species in water. So if you could independently measure the concentrations of OH-, HCO3-, SO4--, etc, etc, etc, then you could report each of those alkaline species in their own molar units. But that is not how TA is measured. The theory behind TA is that you add acid (titrate) a water sample until the pH drops below 4.5 and you report the amount of acid used to neutralize all the alkaline species in the water in units of CaCO3 as if the pH of the water was only affected by calcium carbonate. It is the addition of hydrogen ions (H+) that neutralizes all of the alkaline species. The indicator dye used is designed so that the color transition is at a pH of 4.5 BUT, that particular pH has no meaning on it's own - it's simply the pH below which the carbonate hardness of the water has been transformed into aqueous CO2 gas (which does not affect alkalinity).

To your general question of pH and TA and how to maintain them in a recreational body of water. The answer is that, to a certain extent you could ignore pH and simply measure alkalinity and try to hold that as constant as possible. The human body really doesn't care if it is soaking in water that has a pH of 7.2 or a pH of 8.4 ... no one could tell the difference simply by feeling the water. The only time you would want to care about pH is in terms of calcite saturation - if your calcium hardness were too high and your pH was high, increased temperature could cause calcium scaling to occur. That will most likely occur inside the heater core and, once calcium scale forms, it is mostly insoluble and will not readily go away. Calcium scale inside the heater will reduce efficiency and ultimately reduce the usable life of the heater. While it would rare to find low pH at moderate TA levels, you would still want to ensure that your saturation balance is not too negative as that could lead to corrosion of metal parts. Generally speaking, once the pH drops below 7.0, any kind of ferrous based metals will be subject to enhanced corrosion in a chloride rich environment even when carbonate hardness is present. Sulfates are also bad for most ferrous metals.

When dealing with pH and TA in a pool or hat tub, you always want to adjust those using muriatic acid, not sulfuric acid. Aside from the issues with sulfates in the water, sulfuric acid is a much more dangerous health hazard as it can cause serious skin burns on contact. HCl is much less dangerous to handle and work with.

 

[cfherrman]

Short answer

pH is to control scaling and corrosion issues.

You also want the ta number, not just alkalinity type number.

I'm getting into hydroponics, do you know a good forum?

 

[mrwoo]

As you alluded to, but worth reiterating, pools & spas are NOT horticultural water bodies, so you have to be careful when mixing and applying principles from one to another.

First, some clarification - there is NO hydrogen in CaCO3. And, as far as "alkalinity goes" it is Total Alkalinity (TA) and the results are reported in units of CaCO3 but TA is a mixture of ALL alkaline species in water.......

Hi. Thanks for the detailed reply!

Yes, not H in CaCO3, mistake of words. In cation exchange capacity, the free H2O binds and kicks off elements (depending on valance) so therefore you end with pH changing for root solution area. It is a change in free H in the aqueous solution though, which is maybe what I am trying to grasp. I've spent years and years pouring over articles that reference how the buffering of CaCO3 specifically affects the pH, which in turn is always considered the "keystone" to nutrient uptake when in fact it is the ppm of alkalnity that is soooo much more important.

Let me do some research over the weekend and get back. That was indeed a great reply, very detailed. Thanks for taking the time to type that out.

 

[mrwoo]

Short answer

pH is to control scaling and corrosion issues.

You also want the ta number, not just alkalinity type number.

I'm getting into hydroponics, do you know a good forum?

Oh, not forums really. Actually hemp forums have a lot of great info though. I have a slug of pdf's, mostly from university studies. I would be very happy to share what I have and indeed share what I know. It's 33 years of know nothing to a fine tuned program. I've been at this awhile and love sharing. I wish I had forums that I used but don't.

Thanks for replying.

 

[mrwoo]

As you alluded to, but worth reiterating, pools & spas are NOT horticultural water bodies, so you have to be careful when mixing and applying principles from one to another.

Indeed! Knowing a lot about water in horticulture isn't as much use as I would have thought lol.

First, some clarification - there is NO hydrogen in CaCO3. And, as far as "alkalinity goes" it is Total Alkalinity (TA) and the results are reported in units of CaCO3 but TA is a mixture of ALL alkaline species in water. So if you could independently measure the concentrations of OH-, HCO3-, SO4--, etc, etc, etc, then you could report each of those alkaline species in their own molar units. But that is not how TA is measured. The theory behind TA is that you add acid (titrate) a water sample until the pH drops below 4.5 and you report the amount of acid used to neutralize all the alkaline species in the water in units of CaCO3 as if the pH of the water was only affected by calcium carbonate. It is the addition of hydrogen ions (H+) that neutralizes all of the alkaline species. The indicator dye used is designed so that the color transition is at a pH of 4.5 BUT, that particular pH has no meaning on it's own - it's simply the pH below which the carbonate hardness of the water has been transformed into aqueous CO2 gas (which does not affect alkalinity).

To your general question of pH and TA and how to maintain them in a recreational body of water. The answer is that, to a certain extent you could ignore pH and simply measure alkalinity and try to hold that as constant as possible. The human body really doesn't care if it is soaking in water that has a pH of 7.2 or a pH of 8.4 ... no one could tell the difference simply by feeling the water. The only time you would want to care about pH is in terms of calcite saturation - if your calcium hardness were too high and your pH was high, increased temperature could cause calcium scaling to occur. That will most likely occur inside the heater core and, once calcium scale forms, it is mostly insoluble and will not readily go away. Calcium scale inside the heater will reduce efficiency and ultimately reduce the usable life of the heater. While it would rare to find low pH at moderate TA levels, you would still want to ensure that your saturation balance is not too negative as that could lead to corrosion of metal parts. Generally speaking, once the pH drops below 7.0, any kind of ferrous based metals will be subject to enhanced corrosion in a chloride rich environment even when carbonate hardness is present. Sulfates are also bad for most ferrous metals.

When dealing with pH and TA in a pool or hat tub, you always want to adjust those using muriatic acid, not sulfuric acid. Aside from the issues with sulfates in the water, sulfuric acid is a much more dangerous health hazard as it can cause serious skin burns on contact. HCl is much less dangerous to handle and work with.

So I think I get this now. Let's see. I need to measure the hardness of the water, which is the ppm of dissolved calcium I think. This available calcium then a sort of buffer against excessive foaming in the case of hot tubs and the lack of dissolved calcium would be detrimental because not only would foaming increase but the water would be scavenging any calcium it could find, as in the case of grout and tile. If the dissolved calcium is in the range of 150ppm to 250ppm it is considered ideal for lack of foaming and not interfering with sanitizer effects or etching/scavenging. This is just a basic description I realize, I'm just trying to get to the pH/TA part.

Now we come to the alkalinity. These are the buffers for acid. I've seen in the sticky thread here that it is recommended the TA be 50ppm? If TA is all alkaline molecules that would be about as low as you would ever want to go in the horticulture world as you have removed all the buffer. Granted a plant is different from a body of water, but why is 50ppm touted when most all info I've seen elsewhere to be 80-120ppm? Is that because there is an increase upon agitation/aeriation as I've read? It's a confusing topic if you are really into the details as one article says once you get the TA/pH right it's stable and another says the opposite. I saw also this

However, a high TA requires a low pH to have balanced water.

which doesn't really make sense from what I've experienced, unless there is no CaCO3 in the "high TA"? I take it to mean that if you have a high TA, lets say 400, that you need a low pH, say 6.7. In my world I would drop the alkalinity to my desired level and not worry about the pH (within reason of course) but in a spa world, would you then add some other element/molecule in the water to bring up the pH but not the TA?

Lol, I'm one of those who has to know why. I might need to talk with a chemist, it could be a sickness I have

 

[cfherrman]

With a high ta the pH rises fast, high pH equals red eyes and possible scale build up. Aeration raises the pH which I'm guessing hot tubs get a lot of, so I'm guessing a lower ta to help with that.

Keep the pH in the 7's, this is more important that the ta number

 

[mrwoo]

With a high ta the pH rises fast, high pH equals red eyes and possible scale build up. Aeration raises the pH which I'm guessing hot tubs get a lot of, so I'm guessing a lower ta to help with that.

Keep the pH in the 7's, this is more important that the ta number

Grr, something I'm not getting yet. I've been looking quite a bit, but it must be more complicated than I expect after too many years of relying on the soil media to have such an impact on the solution.

To keep the pH of water with (using my knowledge) a calcium bicarbonate level of 200 ppm down, Hydrochloric acid (muriatic) or sulfuric acid would be used. My water will be at 7.9 to 8.1 pH and 180 - 220ppm of CaCO3, and it will take the pH to about 6.5 to bring the CaCO3 to 80ppm. The "how to use chlorine" guide here states to keep TA at 50ppm. Many guides and manuals say between 80 and 120. So one does ignore the TA then although there is so much information on where to keep it at and how it affects pH and sanitizer?

I guess I'm going to have to get some reagents and borrow some probes from work to see what is going on while I await the delivery of my tub. I've been looking into SWCG over-the-side units and am trying to grasp all of this haha. I'm going to bring an older used fast acting inline pH probe from work and see what it says, along with my digital titrator. I ordered a taylor 2005 kit so we'll see how the TA coincides with my CaCO3 and what the pH does.

I have access to a nice conductivity meter. I think it can do TDS as well. I suppose there is no use for that is there.

Really I've been waiting 20 years for the opportunity to have my own tub, soley for the therapeutic effect on my back, and since I am somewhat of an anal retentive geek I want to keep it running not only as clean as possible but as well and as long as possible.

Thanks so much for taking the time to reply. I appreciate it.

 

[JoyfulNoise]

Any hot tub you purchase, new or used, needs to be purged with Ahh-some first. Biofilms can buildup in the plumbing lines and, in new tubs, the plumbing is pressure tested at the factory but they barely drain the lines which means lots of stagnant water left inside the unit. Purging should be done annually. As well, a tub should be drained and refilled regularly, typically 3-4 times per year. A hot tub is NOT a small pool. It is a very warm body of low-volume water that can build up bather waste, DBPs, and THMs very quickly. The operating temperature of a tub is EXACTLY in the “Goldilocks zone” of bacterial growth for many dangerous pathogens (like legionella). As such, they need to be carefully maintained and regularly cleaned.

 

[cfherrman]

So one thing to remember is the tfp practice is different from the industry. We say I add this to my pool and it does that, we want to exactly know what's happening. The industry just says add this magic in, come back when it makes it worse we will sell you a different magic.

So I say it's best to pretty much ignore all industry recommendations. Tfp recommendations are based on many users use and abuse, and we keep changing them to better suit beginner and veterans alike.

Now I'm not a tub guy so I could have a little error in my advice, but tubs and pools are the same....ish.

So just pretend the TA number is a spring pushing up on the pH, the bigger the number the bigger the spring. Your pH will try to balence with the atmosphere and in my case with sky high ta of 250+ if I add acid down to 7, with a day or two the pH will be back at 7.8-8. Lucky for me my pool is a old cheap Intex and I just get by checking the pH on swim days for eyes. If I had a pool that I wanted to prevent scale on I would have to add acid every couple of days untill the ta got balenced with the atmosphere and then the pH would be stabled. Tubs are different with I'm guessing tons of aeration so letting the ta drop over time is probably a bad idea and setting the ta to a low number helps with rising pH so you have to adjust it less.

In pools and probably tubs the important numbers are FC and pH, the others are important but don't stress over them.

 

[ajw22]

You might want to read what Taylor Technologies says in....

A Spa Is Not A Small Pool

 

[mrwoo]

Any hot tub you purchase, new or used, needs to be purged with Ahh-some first. Biofilms can buildup in the plumbing lines and, in new tubs, the plumbing is pressure tested at the factory but they barely drain the lines which means lots of stagnant water left inside the unit. Purging should be done annually. As well, a tub should be drained and refilled regularly, typically 3-4 times per year. A hot tub is NOT a small pool. It is a very warm body of low-volume water that can build up bather waste, DBPs, and THMs very quickly. The operating temperature of a tub is EXACTLY in the “Goldilocks zone” of bacterial growth for many dangerous pathogens (like legionella). As such, they need to be carefully maintained and regularly cleaned.

Ha! Amazon prime will deliver that Friday along with a Taylor kit and a hach aquachek test strip. I use Hach stuff for work and have always had great results. I dug out the cole parmer meters today and am soaking probes in cleaning solution to calibrate later this week. The tub is still not here so I've got time to figure out exactly what I am dealing with. Tomorrow I will find out the alkalinity via the hach digital titrator and bromcresol reagent and sulfuric acid. For now it's all a comparison of what I know vs what I need to learn.
Thankfully I found this place! I love the way everyone is eager to share.
Regarding bio-film I use chlorine dioxide at work for that stuff, it works sensational although you have to be careful about the ppm level and what material it is compatible with. I'm going to see if any Ahh-some product can be safe for some area's I cannot use that chlor-diox in. I never even heard of it before this forum.

So one thing to remember is the tfp practice is different from the industry. We say I add this to my pool and it does that, we want to exactly know what's happening. The industry just says add this magic in, come back when it makes it worse we will sell you a different magic.

So I say it's best to pretty much ignore all industry recommendations. Tfp recommendations are based on many users use and abuse, and we keep changing them to better suit beginner and veterans alike.

Now I'm not a tub guy so I could have a little error in my advice, but tubs and pools are the same....ish.

So just pretend the TA number is a spring pushing up on the pH, the bigger the number the bigger the spring. Your pH will try to balence with the atmosphere and in my case with sky high ta of 250+ if I add acid down to 7, with a day or two the pH will be back at 7.8-8. Lucky for me my pool is a old cheap Intex and I just get by checking the pH on swim days for eyes. If I had a pool that I wanted to prevent scale on I would have to add acid every couple of days untill the ta got balenced with the atmosphere and then the pH would be stabled. Tubs are different with I'm guessing tons of aeration so letting the ta drop over time is probably a bad idea and setting the ta to a low number helps with rising pH so you have to adjust it less.

In pools and probably tubs the important numbers are FC and pH, the others are important but don't stress over them.

Ohhh you have no idea how much respect I have for peeps who want to know exactly what is happening rather than just parrots! Seriously.
Hmm. That definition is not at all the way I experience dropping alkalinity, at least with H2SO4 and CaCO3. But then I don't have products trying to raise it or aeriation either.

So maybe someone can explain in loose terms. I'll try but it's out my wazoo because it's a theory for now.

CH needs to exist at 150-250 to maintain a level of non-suds and non-etching. (does this affect pH creep or sanitizer affect?)
TA needs to be at say 50? (but, it may be higher depending on the species of alkalinity?)
pH needs to be at 7.5 optimally (but it will creep from aeriation and chlorine?)

So then, to understand it better, what alkalinity is being reduced? Is certain makeups harder than others? For well water would it be better to just get a breakdown of the alkaline species and then understand why it is slow to reduce? If an acid is neutralizing alkaline molecules, what all would cause more to develop? Certain types of chlorine that are calcium based? Is there a rate at which the rise of TA can be seen? Is the CO2 from aeriation adding? I can only assume that if you neutralize the TA uniformly that it only rises again (and pH) if there is more alkaline species introduced.

Also because I am a geek, what about SWCG? Almost every comment I've seen from users state that the pH is very stable comparatively. If you have 250 TA and you reduce it and use SWCG and it remains fairly stable (within reason) what is the difference then? That does not make sense to me, but hey, none of it does yet.

Finally, just how corrosive is an SWCG system on tubs? I'm a handy-man for sure and am not afraid to replace most anything but I can't seem to get a good answer. Lol, the bullfrog website says not to use them but one of the most prominent bullfrog dealers in OKC has a whole page devoted to the use of salt water systems with bullfrogs. If it's any help I bought an R7.

Maybe people just want to dump a cap in and soak rather than truly know what and why, but not me.... I thrive on understanding.

Thanks!

 

[cfherrman]

Ch is just suds/scale, I don't know if any pH effect.

I only mention this paragraph because you like extra information, it's not really needed to know.

Ta as far as pools go(there u go again with the p word) is 1/3 cya and the rest is some sort of bicarb. You only need to adjust your ta number (to remove cya alk number from it called adjusted alk) if your cya is sky high, over 100, and this is just to more accurately manage adding acid in your pool. If I recall a tub should run 20 cya, so moot point even caring about adjusted alk.

The ta number (along with other values) is used to figure water scale/corrosive index, or CSI.

Every time you add fill water, the ta in the fill water will raise the ta. Borax, soda ash, and baking soda all raise the ta and pH in different rates and we prefer aeration to raise pH over a product.

Bleach is pH neutral after a bit of time, all solid clorine is acidic. Swg is mostly said that it does not raise the pH.

The clorine is more corrosive than the water with a little salt in it. A swg needs around 3000-5000 ppm salt, for reference the ocean is 30,000+. Swg get blamed for bad pool management just like red eyes blame on clorine but that actually a pH problem.

Edit, a 1/3 of the cya shows up with the ta test irc

 

[mrwoo]

Ch is just suds/scale, I don't know if any pH effect.

I only mention this paragraph because you like extra information, it's not really needed to know.

Ta as far as pools go(there u go again with the p word) is 1/3 cya and the rest is some sort of bicarb. You only need to adjust your ta number (to remove cya alk number from it called adjusted alk) if your cya is sky high, over 100, and this is just to more accurately manage adding acid in your pool. If I recall a tub should run 20 cya, so moot point even caring about adjusted alk.

The ta number (along with other values) is used to figure water scale/corrosive index, or CSI.

Every time you add fill water, the ta in the fill water will raise the ta. Borax, soda ash, and baking soda all raise the ta and pH in different rates and we prefer aeration to raise pH over a product.

Bleach is pH neutral after a bit of time, all solid clorine is acidic. Swg is mostly said that it does not raise the pH.

The clorine is more corrosive than the water with a little salt in it. A swg needs around 3000-5000 ppm salt, for reference the ocean is 30,000+. Swg get blamed for bad pool management just like red eyes blame on clorine but that actually a pH problem.

Thanks. I do like the extra info.
Couple things. First, do I need Cyanuric Acid if I don't have a lot of direct sunlight? I built an awning off my house on the NE side and put a dual layer polycarbonate cover over it which also filters UV light. Second, if I were to use a SWCG is it correct that I would definately want CYA added?

Now to fun stuff. I tested my water today. I used my Hach digital titrator and Bromcresol Green - Methyl Red reagent powder. Results were 200ppm of CaCO3. According to instructions, I could add the Phenolphthalien and titrate till endpoint (approx 8.4) however, my pH is 7.9 to 8.1 so the P never indicates. The instructions then say that if the result of P (Hydroxide) alkalinity is that basically the TA is the bicarbonate alkalinity, which is 200. It will be interesting to see what the Taylor kit or the test strips say tomorrow night. As of now though my city water is starting at 200 TA and 7.9 pH, CH to be determined. I also know there is chlorine in the water supply. Hach says 3.5ppm can cause color issues with reagents but I happen to have some Sodium Thiosulfate to combat that so it should be a good test between cheap pool kits and more expensive lab type equipment.

After more reading I think I am going to not let the install guys put extra stuff in place, only the filters (meaning no frog ease or ozone etc) so that I can use the Ahhh-some right off the bat. From what I read I will be heating the tub up, adding the Ahh-some and cycling then purging. I did not read if a rinse was required. Then I will fill tub, hit with a shock (not sure what to use for that, presume dichlor granules), kill everything, and then look at a CWCG system. I really have read lots and lots of good reports, understanding it's not a set and forget system at all. I'm not sure on the order quite yet, but whether it's handle CH then TA then pH in certain order seems to be well documented it depends on whether its chlorine/bromine/SWCG first.

another question. When you drain your tub, what do you do with it? That much salt is going to kill plants and will most likely make the soil sterile for years. What about concrete, seems there would be detrimental effects?

Thanks again for all the sharing that goes on here.

 

[cfherrman]

Yes you definitely want a little cya, otherwise the clorine is a bit harsh. Swg is pretty much your supplier of clorine, so almost everything else is the same.

From what i can remember, which this should be in the hot tub startup section, is to use diclor to startup to (I think) 20 cya and then on to your preferred clorine (swg).

When you need a extra boost in clorine, bleach is best, no side effects.

You will have to manage your combined clorimines (cc) and with that I can't tell you because I don't have great information for a tub. It's all over here or someone will be along to guide you about it.

Every kind of alkaline matters so make sure to test for ta, not just one kind.

Deposit test strips into trash, they will let you down.

I would personally work on ta first, like initial fill because personally I have high ta and it sucks in a pool.

Ch should be easy, if you don't have enough use a little Cal hypo for FC + ch. If you have too much use softened water to top up your tub and it won't climb any higher.

 

[mrwoo]

Thanks. I think I have exhausted my original topic and should move on to the appropriate forum section. Thanks to all who responded, I have a much better grasp of what I don't grasp yet lol.

 

[imagineero]

Indeed! Knowing a lot about water in horticulture isn't as much use as I would have thought lol.

That’s quite the understatements. Maybe write this on a couple dozen post-it notes and stick them in places you’ll see them daily to un-learn yourself from applying your existing knowledge to the almost completely unrelated area of recreational water.

Don’t get me wrong, I get where you’re coming from to some extent. I know nothing about hydroponics, but I’m a full time consulting arborist with 10 years industry experience. Soil and water analysis is a topic I have a well formed opinion about, but my knowledge is less than useless in the area of pools/spas; it’s actually harmful or even dangerous to apply, so I intentionally un-link these different worlds and purposely don’t ever use any of my work tools or equipment for the pool.

I’m absolutely a newb to pool world, but it appears from my limited understanding that the function and objectives of pool water are almost perfectly opposed to those of water for plant growth. Water is a nutrient delivery mechanism for plants, and a cornerstone of soil health promotion is to not use chlorinated water. We want to encourage bacterial growth, and keep that thriving complex world of interactions between so many bacteria, fungi, insects, plants and animals alive. In stark contrast to this, water for pools seems aimed more generally at remaining sterile through sanitation, and the other objectives are related to human health, extending the life of equipment it passes through, and preserving the material the pool is made of....

Try to compartmentalise your existing knowledge if you can. Leave your PDFs/research for your work. Take the time to read and understand the extensive and well researched, excellent, and impressively concise knowledge available here. Read every article in the pool school/knowledge base, even the absolutely simplest ones. Try not to analyse them from your current viewpoint, but instead allow them to create a standalone structure of information. A lot of the very good questions you’re asking are well answered there already, in a way that will reveal a clearer path than the answers to the targeted questions you pose.

Oh, and get a magnetic stirrer for the sake of your sanity if you haven’t already

 

[mrwoo]

Yeah, that's pretty much the place I ended up at. Having a functional understanding of how things work for what I needed to know is helpful for sure as a base knowledge set. Without that background I would have to spend a lot of time learning chemistry because I like to know why. As it is I can understand pretty well what is implied even if I did not know it prior. I happen to like putting otherwise useless information in my head, and seeing a larger picture.

And yes indeed I picked up a magnetic stirrer. Honestly I don't know how people can use the color based pH tests. Without my probe I would always see a single shade of pink. Same for the chlorine. I prefer the titrate to endpoint method for sure.

At least I actually enjoy learning it as opposed to seeing it as a PITA!

 

[jseyfert3]

@mrwoo, what you need to start doing is searching this forum for your topic of water chemistry and include "chem geek" in that search. In the past, I've read post after post of amazingly detailed chemical reaction posts. Unfortunately chem geek is no longer active here. Last I heard he is now actively trying to change the outdated and wrong pool industry specifications so all pool users start learning real science like the relationship between CYA and FC. However, there are a wealth of posts he's left behind.

In regards to your question, first off, I'm not an expert. JoyfulNoise is considered to be one of the chemistry experts here. I just happen to be a random guy, who's an engineer, who loves to read on things and have read post after post from chem geek. The essences of your question is that the pH will come to some equilibrium based on the TA level, which is related to CO2. I've read a post from chem geek about the actual chemical reaction, the one that causes pH to rise because of CO2. I will post when I find it, cause I think it's exactly what you want.

In the meantime while I search, check out this table I found from this thread while searching. It shows if the CO2 is in or out of equilibrium at a specified pH and TA level. Note that it's perfectly in equilibrium (so aeration will cause NO pH rise) at a TA of 40 and a pH of 8.0. Note the values are close to 0, so almost in equilibrium, near a TA of 40-50, especially at a pH in the mid to upper 7's.

Oh, and my understanding (very limited as it is) is that CH has little to no effect on pH. It's only relivent for pools and spas as one of the factors used to calculate the CSI index to see if the water will scale (precipitate calcium on surfaces, positive CSI) or rob calcium (eat away stone/tile, negative CSI). For any pool spa that's fiberglass or vinyl, negative CSI is of no concern. You'd only want enough CH in that case to help keep foaming down. I have a CH of ~350 ppm here in Wisconsin but my CSI in my spa is negative. The high CH is therefore of no concern to me.

 

[jseyfert3]

Here's an answer to your reference where you seemed confused as to why a SWCG didn't change the pH of the pool: Pool Water Chemistry

EDIT: That also goes very in depth into the science of FC and CYA, why FC becomes ineffective with increasing CYA, and so why FC needs to be maintained at a fixed ratio of the CYA level. In other words, the very deep chemistry behind this very simple chart: Chlorine / CYA Chart - Trouble Free Pool