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    Thread: pH, KH, GH, TDS, and ORP: what are they and how are they related?

    1. #1
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      pH, KH, GH, TDS, and ORP: what are they and how are they related?

      Thanks to Stephen's wakeup call, I dug back in the Koiphen archived threads. There is a trove of information, and I did learn a lot from past mistakes and successes!

      I also noticed that many people were puzzled about KH, pH, ORP, TDS, and the relationships among them - changing one will affect another. Many add BS (NaHCO3) in the hope to stabilize or boost the KH, pH. Do that to well water in Aurora, NC and you may need to add a truck load before pH goes up to 8.0 (well I exaggerate a bit, but you get the idea). To keep koi in best water condition, some are mindful of low TDS and pH 7, so they tether around 17.5ppm KH and rigorously monitor pH/KH to be on top of any potential pH crash. Others are blessed, and do not see any pH changes. So, what is pH? How to keep water at your desired pH? What affects its value? And how it affects the KH, GH, TDS, ORP? I'd attempt to see if I can somewhat demystify these parametric monsters which have confused many of us.

      On pH:
      First, I'd like to take a deep look into pH. You can find pH 7 in absolutely pure water. That's the definition of pH, and all measurements/equipment are calibrated based on this or traceable to this. The KH and TDS of this water is zero. An example of this pure water is the DI water utilizing to make computer chips in semiconductor wafer fab (where I have the privilege to work since the early 1990).
      When adding impurities (BS, CO2, dead leaves, natural minerals, etc.), the pH changes according to the impurity(ies)'s chemical properties and amount present (concentration) in that water. That's why it is common for someone to experience pH 7 with very low KH & GH (the soft water in Japan), or pH 7.2 and very high GH & KH (for example in Aurora, NC, because of the phosphate buffer - as posted by RickF: https://www.koiphen.com/forums/showt...ht=ro+question), while others experience pH 8+ with a KH of 15+ dKH (we all know 1 dKH/dGH or 1 drop API solution ~ 17.5ppm) and GH of 20+ dGH like Stephen (https://www.koiphen.com/forums/showt...+water+stephen , that's his post about his pH>8; I lost track and still search for his post about KH&GH). Some others use salt softeners to "soften" this water, so they get 15+ drops KH with near zero dGH and pH is still 8+. "Soft" water but dKH is 15+, pH>8, and TDS ~ same as source! Fortunately for fish, in natural ponds (and your seasoned concrete koi ponds) there is a certain amount of KH buffering capacity to resist the acidification (pH drops) and provide a livable condition for fish, as indicated in this graph
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      Problems may arise when the water is deviated from that ideal condition, either intentionally (RO to improve growth/skin) or unintentionally (filtration issues, algae, rain, etc.). That begs the question of what is KH buffer and what happens to it when one encounters pH swing/crash or add BS to counter pH drops. ***This is my first attempt. I will continue my post if you think it is useful information and makes sense. Just let me know***
      Last edited by AkwaKoi; 02-14-2019 at 06:16 AM.

    2. #2
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      I read your post this morning . Keep it up



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      Quote Originally Posted by delbert View Post
      I read your post this morning . Keep it up
      It is great to have someone with his knowledge actually come on this forum and share the knowledge with us. I've been running reverse osmosis and tuyen the op has been with me every step of the way. Everything has been great and a good learning process for me as well.

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      Thanks Delbert and Kevin.

      About KH and its relationship to pH
      Fun fact: Do you know that 1 pH unit is a 10 folds change of the [H+] concentration since pH is defined as the negative log of [H+] concentration? Fish can't cope that easily with a [H+] change of 100 folds, which is 2 pH units.

      All of us know KH is the basicity value due to bicarbonate. Most of our ponds don't have carbonate or (CO3)2- because it only exist in appreciable amount at pH>9. There are many more of those base groups but let's limit our discussion to the carbonate base group for practical reason. To make it easier to understand KH buffer, I use the example of a hamburger fast food restaurant. Suppose each bicarbonate (HCO3- base) ion is a hamburger and each H+ (acid) ion is a hungry customer during lunch rush hours. The "pond" restaurant always has some "base" burgers ready in case any "acid" customer orders. How many "base" burgers this "pond" restaurant has stocked up is the "KH buffer". It will determine how many "acid" customers will be served. Too many "acid" customers order at the same time will deplete the restaurant "buffer" stock, and send the restaurant into frantic mode, i.e. pH crash. When acid is added to our ponds (acids HNO2 or HNO3 from filtration issues, H2SO4 from acid rain, etc.), the bicarbonate is there to combine with the acid to neutralize it and prevents it from turning the pond acidic. When enough acid is added, all the HCO3- is used up, there is nothing left to neutralize and the pond will become acidic. In fact, that's how people measure KH. This is illustrated in the lab with the acid base titration in the curve below.

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      The vertical axis is the pH, and the horizontal axis is the amount of [H+] (that's how chemist write "acid") pouring into the solution being analyzed. The more acid addition, the lower the pH. We usually see things happen between A and B. Ponds rarely have pH above point A which is ~9. Below point B, koi are likely in trouble. [H2CO3 from algae breathing at night or from rain is a bit complicated because it involves the dynamic equilibrium concentrations between three forms of the same base group: (CO3)--, HCO3-, and H2CO3. Let's just treat it as an acid for now.

      Another fun fact: you know that you can put together some color indicator (bromocresol green or thymol blue or both) and a small amount of a strong acid (such as HCl or H2SO4), just enough in each drop to neutralize 5ml of liquid with 17.5 ppm KH in it. That's a KH test solution comparable to API or other KH test products


      ***Please feel free to ask any question and I will be happy to answer them.***
      Last edited by AkwaKoi; 02-17-2019 at 02:34 AM.

    5. #5
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      Back to the burger joint example earlier. If you down size your restaurant, you won't have enough "base" burgers to serve the first wave of "acid" customers. However, if you can make buying burger is illegal, police will be deployed to the "pond" restaurant to arrest many of the "acid" patrons, preventing burger depletion. Reducing TDS will reduce the bicarbonate base, and you will have to be mindful about pH crash, unless you are lucky to have a benign water interaction or you put in place a chemical system to block the reaction and prevent the crash.
      Last edited by AkwaKoi; 02-18-2019 at 03:33 AM.

    6. #6
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      WHAT ABOUT GH and TDS?

      GH is the amount of Ca++ or Mg++ ions in the water. They are the counterpart of KH bicarbonate (HCO3-), but not the only ones. Na+ can also be a counterpart (as in baking soda or sodium bicarbonate) when you add BS to your ponds to bring the pH up. Most incoming tap or well water has Ca++ and Mg++, and usually does not contain Na+. That's why we see high GH goes hand in hand with high KH and high pH (since KH relates to pH as outlined above). Suppose you add calcium chloride to this water, you will have even higher GH, but KH and pH stay the same. Likewise, you will have near zero GH if you use a salt softener to replace all GH with sodium, your KH and pH still stay the same. GH has no relation to pH.

      TDS is the total dissolved solids. It is the conductivity of the water, quantified in ppm or in micro Siemens per centimeter. Pure water is an insulator, with no electrical conductivity. However, don't try to put your hands for too long in pure water charged with high voltage because salt and other contaminants on your skin will leach out, making the water conductive and you will get an electric shock . TDS includes all the carbonates, Ca, Mg, Na, other contaminants in the water, and even fish waste. Therefore, TDS is often higher than GH & KH. Like GH, TDS has no relation to pH.
      Last edited by AkwaKoi; 06-19-2019 at 01:43 AM.

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      ***CORRECTION****
      There are a few errors/obscurities in the previous post, my apology! I guess doing things in a hurry has consequences

      1. "...salt softener to replace all GH with sodium, your KH and GH still stay the same. GH has no relation to pH. "
      should be: "...salt softener to replace all GH with sodium, your KH and pH still stay the same. It is easily seen from these two cases that GH has no direct relation to pH.

      2. From "Pure water is an insulator..." all the way to the end should be: "Pure water doesn't conduct electricity. DI water in the labs/fabs is pure (TDS =0) and its electrical resistance is >18 mega ohms. The dissolved ions (positively and negatively charged: Ca2+, Na+, HCO3-, NO3-, etc.) in water make it a conductor. However, don't put bare hands in pure water charged with 120VAC to test this fact. Salt and other contaminants on your skin will leach out to make water conductive, and you will be electrocuted . The stuffs that make up the TDS reading of your koi ponds are Ca2+, Na+, bicarbonate, all other dissolved constituents in the source water, as well as the dissolved part of your fish waste. TDS number is expressed in ppm of CaCO3; it doesn't matter what are actually dissolved in the water (table salt, baking soda, phosphate, nitric acid, proteins, etc.). TDS is definitely not the combination of KH + GH. If limescale is the only thing that dissolved in the water, the TDS reading in ppm will be identical to the GH which is the weight of limescale. TDS has no direct relation to pH.

    8. #8
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      ABOUT ORP

      Before I get to this topic, I would like to refer you to Stephen's post #2 & #6 in this thread https://www.koiphen.com/forums/showt...high&p=2704319 , post #6 in particular. I also found a short clip about Mike Snaden's early koi pond. Notice the ORP is ~100mV at 1':44" https://www.youtube.com/watch?v=i6viBFdlURU. These two links show that ORP doesn't matter much to good koi keeping.

      ORP is the voltage of your water comparing to the saturated calomel electrode. Simply put, it’s similar to the relative voltage between the terminals of your car battery. The chemical broth surrounding each electrode inside the battery determines whether the ORP of the + post is sufficiently higher than the -post (full) or the reverse (need charging). When charging, the chemicals inside the +post acts like an oxidizer, giving electrons to the -post (reducer). When in use, the chemical inside the +post acts like a reducer, taking electrons from the -post (oxidizer). The actions of the +/- posts outside are the opposite, naturally.

      In our case, ORP reading only matters if we want to zap the dirty organic stuffs with redox reaction in case our pond is not well kept. However, ORP may also change with changing pH. Take the familiar hydrogen peroxide and potassium permanganate as an example.

      When I did my research thesis at school on the dissolution of copper, I used them to analyze my copper solutions. Hydrogen peroxide and potassium permanganate can be both an oxidizer or a reducer depending on whether the pH is high or low, and depending on what else is present in the “water”. ORP can change from high to low with the same “water” sample depending on its pH. According to Stephen, keeping an ORP at 200+ mV can reduce the bad stuffs in the pH range that we, koi keepers, are interested (pH 7 to 8.5). When ORP is too high, even our koi will be zapped which will affect their skin conditions and their health. Stephen recommends 400 top (post #5 in the thread mentioning above).

      This concludes my inputs. I hope you find this thread useful. I am happy to answer any question you may have.
      Last edited by AkwaKoi; 02-22-2019 at 05:01 PM.

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      Ok time to play...

      Like they say kids learn as they play. What I do remember is that when molecules or atoms gain electrons they are said to be reduced. When they loose electrons they are said to be oxidized. Electrons (or the transfer of electrons) really are the currency for energy. They say water is the source of all energy, but the problem with water (H2O) is that it is a very stable molecule and nothing can oxidize it. Nothing... except plants through photosynthesis. A complex molecule called chlorophyll can oxidize it (steal it's electron) with sunlight acting as an agitator. Hence without water and sunlight there will be no life. I hope this explains (to people) what an oxidizer is and what a reducer is to better understand the following questions I have.

      Hydrogen peroxide and potassium permanganate are well known oxidizers (stealers of electrons). Same with bleach, isopropyl alcohol etc. When does hydrogen peroxide and Potassium permanganate act as a reducers? Does that mean PP might not work if your pond's Ph is such and such? What's ph got to do with it? What happens to hydrogen peroxide and PP after it's done oxidizing and does ORP go up or down?
      Time you enjoy wasting is not wasted time. ---- Marthe Troly-Curtin



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      Quote Originally Posted by KoiRun View Post
      Ok time to play...

      Like they say kids learn as they play. What I do remember is that when molecules or atoms gain electrons they are said to be reduced. When they loose electrons they are said to be oxidized. Electrons (or the transfer of electrons) really are the currency for energy. They say water is the source of all energy, but the problem with water (H2O) is that it is a very stable molecule and nothing can oxidize it. Nothing... except plants through photosynthesis. A complex molecule called chlorophyll can oxidize it (steal it's electron) with sunlight acting as an agitator. Hence without water and sunlight there will be no life. I hope this explains (to people) what an oxidizer is and what a reducer is to better understand the following questions I have.

      Hydrogen peroxide and potassium permanganate are well known oxidizers (stealers of electrons). Same with bleach, isopropyl alcohol etc. When does hydrogen peroxide and Potassium permanganate act as a reducers? Does that mean PP might not work if your pond's Ph is such and such? What's ph got to do with it? What happens to hydrogen peroxide and PP after it's done oxidizing and does ORP go up or down?
      Thanks for asking. I like your question very much. In fact, it's the exact same question I asked myself when I did my thesis. Here is my question back to you: If you mix potassium permanganate and hydrogen peroxide together, which one is reduced/oxidized?(and it would be fun if you pause to think/guess for a moment before reading my answer below)

      *************************

      Well, believe it or not, that depends on the pH! I don't remember precisely which ones because it was more than a quarter of a century ago (wow, time flies!!!), but one gives up electron to the other in low pH, and the reverse is true at high pH.

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      I would like to add one word to your statement about water/energy if I may: Water is the source of all living energy. There are a lot more violent [chemical] process that doesn't require water, a recent example is the problem with cellphone battery self burning/exploding. When I was working in the semiconductor wafer fab, the most fearsome fire is not burning/exploding of gasoline, alcohol, acetone, etc. But the spontaneous burning of silane (SiH4) when it is exposed to air. It burns without a visible flame because it is too hot! Not even a blue flame, imagine that!
      Last edited by AkwaKoi; 02-22-2019 at 11:03 PM.

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      Quote Originally Posted by AkwaKoi View Post
      Thanks for asking. I like your question very much. In fact, it's the exact same question I asked myself when I did my thesis. Here is my question back to you: If you mix potassium permanganate and hydrogen peroxide together, which one is reduced/oxidized?(and it would be fun if you pause to think/guess for a moment before reading my answer below)

      *************************

      Well, believe it or not, that depends on the pH! I don't remember precisely which ones because it was more than a quarter of a century ago (wow, time flies!!!), but one gives up electron to the other in low pH, and the reverse is true at high pH.


      Cool, oxidizer wars! From what I learned here, and that is, when PP is too hot of a dose or too hot for a long time they can reverse PP with hydrogen peroxide. Also when applying either pp or hydrogen peroxide on a wound, PP is more caustic leaving permanent scars. So my guess is that PP is a stronger oxidizer. PP will be reduced by hydrogen peroxide. Hydrogen peroxide will be the reducer in this case.
      Time you enjoy wasting is not wasted time. ---- Marthe Troly-Curtin



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      Quote Originally Posted by AkwaKoi View Post
      I would like to add one word to your statement about water/energy if I may: Water is the source of all living energy. There are a lot more violent [chemical] process that doesn't require water, a recent example is the problem with cellphone battery self burning/exploding. When I was working in the semiconductor wafer fab, the most fearsome fire is not burning/exploding of gasoline, alcohol, acetone, etc. But the spontaneous burning of silane (SiH4) when it is exposed to air. It burns without a visible flame because it is too hot! Not even a blue flame, imagine that!
      I knew I was missing a qualifier somewhere
      Time you enjoy wasting is not wasted time. ---- Marthe Troly-Curtin



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      Quote Originally Posted by KoiRun View Post
      I knew I was missing a qualifier somewhere
      Hey, that's very unfair. It's the fish I intend to fry for my dinner, and look what you do to it

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      Quote Originally Posted by KoiRun View Post
      Cool, oxidizer wars! From what I learned here, and that is, when PP is too hot of a dose or too hot for a long time they can reverse PP with hydrogen peroxide. Also when applying either pp or hydrogen peroxide on a wound, PP is more caustic leaving permanent scars. So my guess is that PP is a stronger oxidizer. PP will be reduced by hydrogen peroxide. Hydrogen peroxide will be the reducer in this case.
      It's more like a who is stronger contest, "refereed" by the Nernst equation with the set of rules based on their standard electrode potentials. And there is also a home field advantage: supposed we are both strong, and we fight outdoor in the middle of winter in Mississauga bare chest, I would loose (or die before the match ends). If you fight in the Mohave desert in the middle of summer, I have my field advantage. Oxidizing or reducing is sometimes very dependent on the external conditions. I hope I make sense

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