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Gh testing

Discussion in 'General Plant Topics' started by PaulB, Aug 28, 2005.

  1. PaulB

    PaulB Subscriber

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    Hi Tom, did a test today adding 1/2tsp of MgsO4+7H2O (epson salts) to 20 lt (5g) of tap water and it raised Gh by 4dGh or 71ppm. Also performed the same test with 1/2tsp of CaCl2 and it raised the Gh by 6dGh or 107ppm. thest tests were done using a new Aquarium pharmacuticals Gh/Kh test kit and they were way above the results predicted by either the Fertilator or Chuck Gadd's calculator. The question is which is correct :confused: I tested water before and after to determine the effect of adding these chemicals. :confused: :)
     
  2. Spar

    Spar Guru Class Expert

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  3. PaulB

    PaulB Subscriber

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    Re: Gh testing

    Talk about confussing, in other words adding CaCl2 & MgSO4+7H2O in the quantities described in my post, i actually have 2.8dGh/51ppm not 10dGh/179ppm as my test kit tells me. Is there Gh test kits avaliable that will indicate the correct Gh value when adding these chemicals??? :confused: :) and the ratios are 4:1.
     
  4. Spar

    Spar Guru Class Expert

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    Re: Gh testing

    i guess the only way is to go out and buy the Lamotte Calcium testkit.

    Did you derive from the answers in the post that we have to just ignore the GH testkit results now when dosing CaSO4 and MgSO4?

    I really just needed to know that if I dose 36ppm Ca &/or Mg, and my GH testkit claims I rose GH by 140ppm, I now have to totally ignore the GH testkit, correct?

    This was the first I had heard of the 2.5 and 4.1 divisions, but it makes sense.
     
  5. PaulB

    PaulB Subscriber

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    Re: Gh testing

    yes i did derive that we have to disregard the results of the test kit and rely on the results from the calculators. this is frustrating because i will have trouble making others in our plant (and aquarium) group understand that their Gh test kit lies to them about the real Gh of their tanks. Like Tom i have the problem of enlightining the plant & aquarium groups that i am involved with in australia that alot of the information regarding growing aquatic plants is false. (ie nitrate & phosphate levels. etc). also the lamotte test kits are not available in australia. :rolleyes:
     
  6. Tom Barr

    Tom Barr Founder
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    Re: Gh testing

    The amount of opposition does not matter if you are right.

    1.
    Suggest that they do not believe you, suggest they try it for themselves then they will know........

    2. Ask why does SeaChem, Kent, ADA, Lush gro and many other plant fertilizer companies make such PO4 and NO3 additive products for planted tanks?

    3.
    Ask the question, if as they say, suppoose NO3 and PO4 excess causes algae, why when I add KNO3/KH2PO4, I have no algae then.

    Accordingly to them and their theory, I should have algae/algae bloom yet it does not appear.

    If as they say it causes algae, where is your algae?
    For the theory to hold true, you need to have the theory actually hold up when add these nutrients.

    Otherwise it's not much of a theory..............
    Sort of a very basic thing.........

    I'm not saying what causes the algae not to grow, that was not the question, I am saying that adding PO4/NO3(or GH, Traces) excess does not cause algae as they claim.

    If it did, we should all have algae.

    I generally do not change my dosing routine if things are going good, but if I test and I get a off reading that seems strange, I'll look into it more and re set the tank with a water change, test the tap as well and see how close the test kit is or is not to a standard.

    I do not change my dosing routine based on the test kits as a rule.
    I change the dosing routine in response to the plants.

    I know, and it does not take that long to learn this, when the plants are slowing down and pearling less.

    So you can guess and add more Trace/PO4,NO3 etc and/or you can re set the tank with water changes etc.

    You can also "guess" about 24 hours before a water change very safely!!
    Then see the response of the plants. Generally, most larger issues will perk the plants up if you added something the day before, so right before your water change, you'll know if that addition of KNO3 yesterday was what you lacked.

    This is a rapid safe method to learn plant responses when things slow down in the tank for unknown reasons near the end of the week etc.




    Regards,
    Tom Barr
     
  7. Joe Bloggs

    Joe Bloggs Junior Poster

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    Re: Gh testing

    First time on here so "Hi everyone." I hope I'm following this thread correctly. If you are looking to increase your GH by 36ppm at a ratio of 4:1 Ca to Mg, you would add 10ppm Ca & 2.5ppm Mg. Hope that helps.
     
  8. Spar

    Spar Guru Class Expert

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    Re: Gh testing

    hmm.. i interpreted it as that you would still increase Ca:Mg by 27:9 (total of 36ppm), but just ignore the fact it appeared GH increased by 103ppm. in other words, the "actual" GH increase was still only 36ppm.
     
  9. Tom Barr

    Tom Barr Founder
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    Re: Gh testing

    What we add:

    CaSO4 * 2H2O
    MgSO4 * 7H2O

    They are hydrated..............

    GH measures Mg/Ca, not the H2O..........
    That may be the source of the error/confusion........

    Regards,
    Tom Barr
     
  10. Spar

    Spar Guru Class Expert

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    Re: Gh testing

    I really do usually understand stuff pretty quick, but this is still confusing me for some reason.

    So I will let someone pick out the "correct" scenerio:

    factors:
    Beginning GH = 85ppm (from tap)
    Per Fertilator - added (CaSO4)2.H2O & (MgSO4)7.H2O = 22ppm
    Ending GH testkit reading in tank = 148ppm

    That said. What is my "true" Ca/Mg content in my tank (lets assume here that the original 85ppm is fully Ca/Mg):

    1) 107ppm (85 + 22)
    2) 148ppm

    I think it is 107ppm. Regardless of what the GH testkit says. The answer to this will either 1) confuse me to extreme :gw or 2) make me feel smart once again :cool:
     
  11. Joe Bloggs

    Joe Bloggs Junior Poster

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    Re: Gh testing

    Adding ppm of Ca plus Mg doesnt give you GH. I believe hardness is a measurement originally based on the amount of calcium carbonate in water, of which the actual amount of Ca makes up only part of that. Spar; on an earlier post you mentioned 2.5 & 4.1 divisions. As an example...in the town where I live the local council has given me a report on our tap water. It has a hardness of 92. It has 21ppm calcium & 9.6ppm magnesium. Multiplying the Ca amount by 2.5 and the Mg amount by 4.1 gives me the GH. In your case you increased your GH 63ppm. You said you added 22ppm Ca and Mg .
    That could have been made up of 17ppm Ca & 5ppm Mg. 17x2.5=42.5 5x4.1 =20.5. A total of 63ppm GH.
     
  12. Spar

    Spar Guru Class Expert

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    Re: Gh testing

    My understanding was that Ca + Mg does = GH. My water report also has Hardness (specifies from CaCO3) and Calcium (stand alone) seperate. I never did understand why Ca + Mg doesnt equal that Hardness level. I guess what you said explains it a little.

    So if my GH increase = 63ppm
    I added Ca and Mg = 22ppm

    What is the other 41ppm (63 - 22)? Can't be CaCO3 as I didn't add any.

    My thoughts is that a GH testkit assumes that any trace of Calcium is "assumed" to be from CaCO3 of which gives a different Calcium ppm than does CaSO4 or CaCl2 per gram added... thus a somewhat ineffectiveness in the testkit itself.

    This is really giving me a headache trying to decifer it!
     
  13. Tom Barr

    Tom Barr Founder
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    Re: Gh testing

    Okay, I'll save you guys.

    GH is a funky unit and KH is also well, blame it on them Germans.

    1 degree GH = 18 ppm CaCO3 = 18 mg/L CaCO3 = 18 mg/L MgCO3
    (I assume its the same for mg/L for Mg.)

    Now to convert that to mg/L of calcium only we go to the periodic table
    and look up the atomic weights as follows:

    Ca = 40
    CaCO3 = 40 + 12 + 16*3 = 100

    Therefore:
    1 degree GH = (18 mg/L of CaCO3) * (40 units Ca) / (100 units CaCO3)
    = 18 * 40 / 100 mg/L of Ca
    = 7.2 mg/L for Ca

    Similarly:
    Mg = 24.3
    MgCO3 = 84.3

    Therefore:
    1 degree GH = (18 mg/L of MgCO3) * (24.3 units Mg) / (84.3 units CaCO3)
    = 18 * 24.3 / 84.3
    = 5.2 mg/L for Mg


    Now if I look to my water chemistry:
    Water Supply Analysis
    Total alkalinity 30 mg/L
    Total Hardness 76 mg/L
    pH 8.0
    Calcium 20.6 mg/L
    Magnesium 5.62 mg/L

    I can calculate the GH as follows
    Calcium: 20 mg/L / 7.2 mg/L/degree GH = 2.86 degrees GH
    Magnesium: 5.62 mg/L / 5.2 mg/L/degree GH = 1.08 degrees GH
    Total: 2.86 + 1.08 = 3.94 degrees GH

    Questions?

    Here's some of us older bone heads wading through it also:
    http://www.thekrib.com/Plants/CO2/units.html#0

    Use molar concentrations folks!!!

    Regards,
    Tom Barr
     
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