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Trying to understand Kh and GH

Discussion in 'General Plant Topics' started by sandeepraghuvanshi, Jul 6, 2012.

  1. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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    I need some help in understanding water test parameters.
    My water test report mentions;

    Calcium as Ca mg/l 82
    Magnesium mg/l 75
    Total Alkanity mg/l 323

    Total Hardness mg/l 520
    as Caco3

    Now what will be my Kh & GH in dH

    GH- General hardness-= (Total Hardness)/17.89=520/17.89=29.06 dH

    KH- Carbonate hardness= (Total Alkanity)/17.89= 323/17.89= 18.06

    Are these calculation correct??
     
  2. Biollante

    Biollante Lifetime Charter Member
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    Yes You Are Correct--Ol' Gasbag Answer below

    Hi,

    Yes within rounding errors, you are correct I calculate Total Hardness (GH) as follows.
    Given (your numbers) Calcium as Ca[SUP] mg[/SUP]∕[SUB]l[/SUB] 82, Magnesium [SUP]mg[/SUP]∕[SUB]l[/SUB] 82

    • M[SUB]CaCO[/SUB][SUB]₃[/SUB]∕M[SUB]Ca[/SUB]=[SUP]100.1[/SUP]∕[SUB]40.1[/SUB]≈ 2.5; M[SUB]CaCO₃[/SUB]∕M[SUB]Mg[/SUB]=[SUP]100.1[/SUP]∕[SUB]24.3[/SUB]≈ 4.1
    • [CaCO[SUB]3[/SUB]]= 2.5[Ca[SUP]2+[/SUP]] + 4.1[Mg[SUP]2+[/SUP]]
      • [CaCO[SUB]3[/SUB]]= 2.5[82[SUP]mg[/SUP]∕[SUB]l[/SUB]] + 4.1[75[SUP] mg[/SUP]∕[SUB]l[/SUB]]
      • CaCO[SUB]3[/SUB]=513[SUP] mg[/SUP]∕[SUB]l[/SUB]
    • 513[SUP] mg[/SUP]∕[SUB]l[/SUB] CaCO[SUB]3[/SUB]∕(17.9[SUP] mg[/SUP]∕[SUB]l[/SUB] ∕dGH)≈28.7-dGH
    The 7[SUP] mg[/SUP]∕[SUB]l[/SUB] difference in the calculated Total Hardness (GH) and stated totals could be rounding errors, otherwise it implies there are other +2 valance elements present.

    Biollante
     
  3. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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    Thanks.
    That is a big relief.
    You have used a ratio of 2.5 Ca, 4.1 Mg, can you please explain this ratio.
    I had done a detailed calculation using atomic weights and molar weights, is it same the thing?
    I don't have it right now, will check it in evening.
    Although not very relevant but I do try to understand these concepts, and this is what makes the hobby interesting for me.
    By profession I am a Chartered Accountant, but the hobby has made me read biology, physics, chemistry and even philosophy.
     
  4. Biollante

    Biollante Lifetime Charter Member
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    Parallel Hobby

    Hi,

    M[SUB]CaCO₃[/SUB]∕M[SUB]Ca[/SUB] simply give us the mass ratio (M often is "mass") to convert Calcium to the Calcium carbonate equivalent.
    From my Periodic Table of the Elements (inside cover of my not-that-out-of-date copy of CRC Handbook of Chemistry and Physics, 86[SUP]th[/SUP] edition)
    • I find that Calcium, Ca has an atomic weight of 40.078, which I round of to 40.1,
    • likewise I find Carbon, C has an atomic weight of 12 (12.0107),
    • Oxygen has an atomic weight of 16 (15.994).
    • While I am at it I also find that Magnesium, Mg has an atomic weight of 24.3 (24.3050).:)

    Now I find the atomic weight of Calcium carbonate, CaCO[SUB]3[/SUB] is 40.1 + 12 + (16 X 3) = 100.1

    M[SUB]CaCO₃[/SUB]∕M[SUB]Ca[/SUB] = 100.1 ÷ 40.1 = 2.5, now I know that the Calcium equivalent of Calcium carbonate is 2.5 X [Ca[SUP]2+[/SUP]] (brackets generally indicate a quantity).
    M[SUB]CaCO₃[/SUB]∕M[SUB]Mg [/SUB]= 100.1 ÷ 24.3 = 4.1, now I know that the Magnesium equivalent of Calcium carbonate is 4.1 X [Mg[SUP]2+[/SUP]]

    Given (your numbers) Calcium 82-[SUP]mg[/SUP]∕[SUB]l[/SUB], Magnesium 75-[SUP]mg[/SUP]/[SUB]l[/SUB] we have quantities.
    Therefore [CaCO[SUB]3[/SUB]]= 2.5[Ca[SUP]2+[/SUP]] + 4.1[Mg[SUP]2+[/SUP]]
    Plug in the numbers [CaCO[SUB]3[/SUB]]= 2.5[82[SUP]mg[/SUP]∕[SUB]l[/SUB]] + 4.1[75[SUP] mg[/SUP]∕[SUB]l[/SUB]]
    We find the Calcium and Magnesium portion is CaCO[SUB]3[/SUB]=513[SUP] mg[/SUP]∕[SUB]l[/SUB].:)

    Then to convert [SUP]mg[/SUP]∕[SUB]l[/SUB] to German degrees of hardness we divide the result by 17.9[SUP] mg[/SUP]∕[SUB]l[/SUB] ∕dGH.
    513[SUP] mg[/SUP]∕[SUB]l[/SUB] CaCO[SUB]3[/SUB] ÷ 17.9[SUP] mg[/SUP]∕[SUB]l[/SUB] ÷ dGH = 28.7-dGH

    I am a bit curious about the 7[SUP] mg[/SUP]∕[SUB]l[/SUB] difference in the calculated Total Hardness (GH) and stated total. It could be rounding errors, I suppose, it just is not an obvious one, if it is a rounding error. It implies at least one other +2 valance element present.:rolleyes: :)

    Any way I hope this helps.:cool:

    Biollante
     
    #4 Biollante, Jul 7, 2012
    Last edited by a moderator: Jul 7, 2012
  5. Biollante

    Biollante Lifetime Charter Member
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    Many Ways to Enjoy the Hobby

    Hi,

    I should add, most folks use a Molar Mass Calculator and calculating general hardness can be done with a Water Hardness Calculator.
    :)

    I know I annoy many folks with all this stuff, but that is my parallel hobby.
    :highly_amused:

    In a time of all these calculators I do not think it hurts to understand how we get the numbers we use.
    :cool:

    Biollante
     
  6. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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    I suffer from same disease;)
    Now I am trying to calculate carbontes using same methods, but I getting a total of 235.84 insteadof 323.
    I am getting as follows
    Co3 from cacao3= 136.78
    Co from Mgco3 = 99.06
    Total 235.84

    This leaves a gap of 87.16.
    Now are there more carbonates other than caco3 and mgco3.
    Or other acids are repsonsible for alkanity.
    Hope I am not boring you or others.
    I have a excel sheet for the same, don't know how to attach it.
     
  7. Biollante

    Biollante Lifetime Charter Member
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    I Love This Stuff, How I earned The Title: Ol' Gasbag... Folks Around Here Hate It!

    Hi,

    This is where the use of equivalents causes confusion.
    :gw

    We measure general or total hardness with CaCO[SUB]3[/SUB], which are +2 valance (oxidation state) elements, predominantly Calcium and Magnesium, none of these contribute to carbonate hardness (at aquarium pH), and more correctly called alkalinity.
    :)

    Alkalinity is stated in terms of Calcium carbonate, CaCO[SUB]3[/SUB] as well but can consist of only hydroxide (OH[SUP]-[/SUP]), carbonate (CO[SUB]3[/SUB][SUP]2-[/SUP]) or bicarbonate (HCO[SUB]3[/SUB][SUP]-[/SUP]).

    In our aquariums, we seldom concern ourselves with hydroxide (OH[SUP]-[/SUP]) also known as lye as it exists only above pH 10.

    Carbonate exists predominantly from pH 8.3 to pH 10, much is made of the fact that carbonates can exist down to pH 7, based on my reading and limited experience from pH 8.3 to pH 7, carbonates account for less than 1% of total alkalinity and the closer to pH 7 much, much less than 1%.

    In normal planted aquariums bicarbonate (HCO[SUB]3[/SUB][SUP]-[/SUP]) is going to be 99% of the alkalinity, it does not hurt to remember that things such as ammonia, borates, silicates, anything with acid/base properties present in significant concentrations, will cause the calculated concentrations of bicarbonate to be in error.

    In our aquariums it is the use of phosphate buffers, products such as pH Up, pH Down, pH Sideways, Discus Buffer and so forth that cause the most problems.:rolleyes:

    [HR][/HR]
    All of that was the Ol’ Gasbag setting you up for the direct answer:
    :p

    “Total Alkanity mg/l 323” provided in your original post only describes total carbonate hardness without more information I have no way determining species present.

    If the sample water is less than pH 7 and assuming no significant concentrations of acid/base combinations, then I could say that the alkalinity is bicarbonate.

    Then I can use our mass ratio to find the amount of bicarbonate present.
    :calm:

    The total weight of HCO[SUB]3[/SUB][SUP]-[/SUP] is 1 + 12 + (3 X 16) = 61

    M[SUB]CaCO₃[/SUB]∕M[SUB]HCO3[/SUB][SUP]-[/SUP] = 100.1 ÷ 61 = 1.6
    323-[SUP]mg[/SUP]∕[SUB]l[/SUB] CaCO[SUB]3[/SUB] = 1.6[HCO[SUB]3[/SUB][SUP]-[/SUP]]
    202-[SUP]mg[/SUP]∕[SUB]l[/SUB] HCO[SUB]3[/SUB][SUP]-[/SUP]
    :cool:
    Biollante
     
  8. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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    Thanks a lot for your answers.
    One of my main reasons for all this is that I use underground water and the test report is as follows

    pH 7.56
    Colour Hazen
     
    #8 sandeepraghuvanshi, Jul 8, 2012
    Last edited by a moderator: Jul 8, 2012
  9. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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    Till I get my test kits, can someone tell me what will be the GH and Kh of RO water?
    I am getting a TDS reading of about 50 with my TDS meter, I know there is no direct relation between the two.;)
     
  10. Biollante

    Biollante Lifetime Charter Member
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    Time to Calibrate That TDS Meter!

    Hi,

    That is hard water!:rolleyes::highly_amused:

    I would not expect scum on the water as much as salt creep from such water.:)

    Reverse Osmosis water should be close to zero TDS, GH, KH, and about pH 7.:)

    I would definitely have filtration ahead of your RO filter.

    Actually, the water is not as bad as you may think; many plants and critters will do just fine.:gw

    Your TDS meter should be reading 1270-[SUP]mg[/SUP]∕[SUB]l[/SUB] or ppm Calcium and Magnesium accounts for 157-[SUP]mg[/SUP]∕[SUB]l[/SUB] (ppm) of TDS, your alkalinity (KH) accounts for another 202-[SUP]mg[/SUP]∕[SUB]l[/SUB] (ppm) of TDS in your water.

    • Another way of looking at TDS (total dissolved solids) should be the total of all the “stuff” in the water, there are a few rules, but if you have a list of how much of everything is in the water, it is simple addition.

    If “50” is an accurate TDS reading and your water report is correct, the water you are sampling is highly filtered and quite usable.:calm:

    Biollante
     
  11. Biollante

    Biollante Lifetime Charter Member
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    2:1 OK, 3:1 or 4:1 RO:Tap Water Better...

    Hi,

    A correction, my apologies, sometimes I spend so much time looking at the trees and I miss the forest.
    :eek:

    A TDS of 1270-ppm is 1.27 parts per thousand and anything over 1-ppt is too high for most freshwater plants and critters, aside from some Lake Tanganyika or Lake Malawi critters. Generally as TDS reaches 500-ppm or 0.5-ppt some of the "rules" change.
    :)

    I think the RO water is a good idea and I would recommend at least 2-parts RO to 1-part tap, 3 or 4-parts RO to 1-part tap water is even better.
    :)

    Biollante
     
  12. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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    It has been a week since I got ph & tds meters.
    I have been testing on a daily basis, the average of reading is as below

    Parameter | Source - | RO | Aquarium
    PH | (7.6 to 8.2) - | ( 6.8 to 7.1) | ( 6.2 to 6.5)
    TDS | (1150 to 1220) | (48 to 51) | (870-890)

    All readings at taken in evening.

    Now I am changing 80 lits of water every week, out of this 50 lit is RO water about 63%.
    I think I will wait for my GH, KH test kits, and then decide if to change the ratio of RO water
     
    #12 sandeepraghuvanshi, Jul 8, 2012
    Last edited by a moderator: Jul 9, 2012
  13. Biollante

    Biollante Lifetime Charter Member
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    You Do Not Need Test Kits To Figure This One, More RO OR Brackis OR African Cichlids

    Hi,

    You are going to need to do substantial water changes to get TDS under 500-ppm. I suspect you will be much happier once you get into the 200-250-ppm TDS.
    :)

    With or without test kits of any sort you will need to increase the percentage of RO water, the tap water information alone is enough to go on. Unless you want a brackish aquarium or Lake Malawi African Cichlid tank, I am partial to Lake Malawi Cichlids myself. I do not have much experience with Lake Tanganyika critters but they are spectacular as well.

    I will treat the ranges you provided as averages by adding the two numbers you provided by two. To provide an average I need all of the numbers.

    The 80-liters you are using to change the water still has a TDS around 475-ppm.
    ;)

    Since I do not know the size of your aquarium all I know is the net reduction of 710-ppm for the 80-liters replaced. If it is a 100-liter aquarium, you will be in passable shape in a couple of weeks.
    :)

    An RO system ought to be able to knock the TDS down to single digit parts per million. Your RO may require a new membrane; a good charcoal block filter in front will help preserve the membrane as will a pump to ensure proper pressure across the membrane.
    :cool:

    Biollante
     
  14. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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    Tank size is 36X18X18, leave aside substrate 2", water voume is 170 lit.
    Wc every week 80lit = 50 lit RO+30 lit Tap water.

    Source water Gh 520 ppm, Ro 50 ppm(need to confirm this once test kits arrive)
    I started on 1-6-2012,
    gh on 7-6-2012-= 382
    I have calculated it by (90*520+50*50+30*520)/170

    So after one month gh should be 238ppm or 13.32
    Do you concer with my calculations.?;)
     
  15. Biollante

    Biollante Lifetime Charter Member
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    I Will, For A Small Fee, Be Happy To Validate Just About Anything

    Hi,

    I may be confused, happens pretty regularly, but…:eek:

    While I agree (90*520+50*50+30*520)/170 = 382, I do not understand the relevance or where the 238ppm GH comes from.:eek:

    I was under the impression the “50” (ppm is my assumption) was TDS. I have no way of knowing the percentage of Calcium and Magnesium in the 50 (presumed ppm) TDS reading.:eek:

    I think you are inferring (from post #8) that since total hardness was 520-ppm GH and TDS was 1270-ppm that since (520 ÷ 1270) X 100 = 41% so 41% of 50-ppm RO water (20.5-ppm) must be GH.

    Even assuming that you get the general hardness down to 238-ppm GH, 46% of its original level that means alkalinity is still 149-ppm KH. Total dissolved solids, TDS is still going to be 584-ppm (0.584-ppt).

    The problem is the total amount of stuff in the water.:gw

    My sense is that you have made up your mind a certain mix of RO. You are of course free to do as you please.

    Anyway, my advice is 3 or 4 parts RO to tap water without regard to test kits or results that is just the arithmetic. In fact, save your money on test kits and invest in filtration.

    Best of luck,
    Biollante
     
  16. Biollante

    Biollante Lifetime Charter Member
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    A little more calculating

    Hi,

    The cation and anion do not really add up.:eek-new:

    I suspect there is something like 335-ppm of Sodium in there as well, even with that added the analysis is off.:(

    I also calculate the osmotic pressure 82.08-kPa, so that would require an operating pressure for an RO membrane of 228-kPa, the reason your RO is only getting down to 50-ppm TDS is that it is a freshwater membrane and it appears you require a brackish or seawater membrane.:(

    Or some good filtration in front of the RO filter.

    Biollante
     
  17. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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    First of all tanks a lot for applying that much time to my posts.
    Now as I do not have a gh test kit, I do not know the gh or kh of my Ro water, so just for calculation purpose I have used 50 as gh also, ( a fool's assumption;), I know)
    Now TDS of my aquarium water is 800-900, seems to vary a lot, is temp a issue here.
    Now you have advices 60-75% of RO water, now is this % of water change I am making or to the total water in aquarium.
    Currently I am mixing 50 lit of Ro water with 30 lit of tap water, which gives me a ratio of 63%
     
  18. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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  19. sandeepraghuvanshi

    sandeepraghuvanshi Prolific Poster

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  20. Biollante

    Biollante Lifetime Charter Member
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    Some People Like Suduko, Some Crosswords, Me I Like Annoying People...

    Hi,

    You are welcome!
    :D

    I do not mean to be aggravating,
    :eek: I just am.:eek: Some situations catch my attention and I like to understand.
    • It really is just arithmetic.:)

    I think you need to do a series of large water changes to get to a point where 75-80% of the water is RO.

    • The reason for a series of water changes is to avoid shock to the critters and biological filtration.;)

    The fact is that as your tank is now brackish.

    Mollies are a good choice as they are critters that do well in brackish water, it may not be necessary to bring the water all the way down, if you choose plants and critters that tolerate higher osmotic pressures.

    It is important to get under 500-ppm (0.5-ppt), from what I see in your tank and based on your description getting under TDS 400-ppm would be great.

    • 450-ppm TDS is a little over 2-parts RO to 1 part tap (66.66%).:)

    Your RO device is a bit underpowered, I calculate you would need 228-kPa the unit you have is capable of 196-kPa so 50-ppm TDS is probably doing quite well. The higher the input water temperature generally the less efficient the filter, yours claims input water temperature up to 45°C, my guess is the efficiency is somewhat lower at the high end.

    Are you using the "high TDS" membrane?

    Is the water chlorinated?
    :confused:

    Is the tap water microbiologically safe? I bring this up only because I see they advertise

    • “It also helps protect your family from water-borne disease-causing bacteria, viruses and protozoa. It also eliminates harmful disease-causing chemicals like pesticides and more, ensuring that every drop of water your family drinks is pure and safe.”

    If 50-ppm TDS can get through, then so can other stuff. I caught the Silver Impregnated, to kill protozoans, I cannot find any information, explaining how it works (how much silver enters the water column) this could be suppressing your biological filter that would help explain the scum.

    My assumption is that they are using standard 2.5 inch TFC Spiral RO Membrane, so you should be able to replace it with a brackish water membrane, which will lower the pressure required and you should be able to get down into the single digit TDS.
    :)

    Biollante
     
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