Water Chemistry - High GH with Mg / K deficiency?

Discussion in 'Water Chemistry' started by Hoejay, 7 Jan 2008.

  1. Hoejay

    Hoejay Member

    29 Oct 2007
    I have a goal to get a fully planted tank going with moderately high lighting, EI & CO2. I have a tank spare approx 22 usg. I would like to use straight tap but I fear the problem with the water is its high GH 180dH with deficiencies in K unknown & Mg 0.1mg/l.

    When I read the plant adds it seems there are conflicts between ideal light and or water requirements. Do you select your on plant mix water parameters KH & GH?.

    Possible Planting
    Hemianthus Callitrichoedes and / or Glossostigma Elatinoides / Micrantheum Umbrosum
    Sagiteria Lileoptris,
    Echinodorus Tenellus

    Could all these be started emersed (style.) what is the recommended planting density to achieve a carpet of plants?

    Dimensions 79(l) x 27(w)x 37(h)
    Lighting 2x 24w T5 1x20w T8
    Substrate 1-2mm quartz gravel over JBL Aquabasis Plus
    Decor Rock & drift wood branches
    3-4 weeks terrarium
    Add water.
    EI ferts.
    Temp 20-240C
    Jewel internal filter
    DIY CO2, pressurised or yeast? to be added via powerhead

    Would cutting with RO then adding a GH boost be a better alternative to boosting the tap deficiencies and further increasing the GH.

    Are specified hard or soft water plants adaptive to non ideal conditions?

    How much Mg should be added to avoid deficiency in the plants, 10mg/l?

    What is the relative composition of GH boost (Ca/K/Mg/Fe SO4), would adding a recommended ½ tsp per 100ltr of GH boost add sufficient Mg?

    Or knowing that I have more than enough Ca but unknown K will dosing tap with Epsom salts for Mg be sufficient with a small increase in GH.

    Is there a relationship between Conductivity, Total hardness and TDS?

    On adding Nitrate & Phosphate nutrients, if 17.8ppm = 10dH should we see a rise in GH of “X”0dH would this be an equivalent to a rise in TDS which can be read to1ppm?

    Here’s the data

    Local Water Parameters given by South East water company

    GH = 17.60dH
    pH = 7.4
    Ca = 125.9 mg/l
    Na = 28.9 mg/l as Nitrate, chloride or Carbonate?
    K = ?? mg/l as Nitrate, Sulphate or Carbonate?
    Mg = ?? mg/l as Sulphate?
    B = 0.1mg/l
    Mn = 2.0µg/l
    Fe = 34.0µg/l (unusual max reading affecting average, low value is 12)

    Nitrates = 23.4 mg/l
    Chlorides = 42.7 mg/l
    Sulphates = 49.2 mg/l
    Phosphates = ?? mg/l
    Total disinfectant = 0.3 mg/l
    Conductivity = 652.3µs/cm

    “Total hardness GH” given by water company is

    CaCO3 = 314.8 mg/l = 314.8 x 0.056 = 17.60dH

    Mg by calculation [Ca x 2.497 + Mg x 4.188] x 0.4 = Ca CO3 mg/l

    {314.8-[125.9 x 2.497]}/4.188 = 0.1

    Mg = 0.1 mg/l (very low, PCV of water authorities can be up to 50mg/l)
    Adding 0.1gm/l MgSO4 would raise GH by 0.60dH?
    If carbonate hardness KH the difference between Total hardness & Permanent hardness

    Total Hardness = 314.8 mg/l

    Permanent hardness
    Nitrates = 23.4 mg/l
    Chlorides = 42.7 mg/l
    Sulphates = 49.2 mg/l
    Phosphates = ?? mg/l

    Total Permanent hardness = 115.3 mg/l

    KH Carbonate Hardness = 199.3 mg/l = 11.20dH

    PH, KH & GH measured at tap with test kit would approximate to values given by Water Company.

    Any advice welcome

  2. Ed Seeley

    Ed Seeley Member

    3 Jul 2007
    First of all I think you should be fine with the plants you listed in harder tap water.
    All the plants you listed should grow well emersed.

    All seems fine. I'd go for pressurised if possible as you have much greater control.

    Most plants seem to grow fine in harder water despite being from naturally softer conditions. Some, such as Rotala wallichi and a few others won't do as well though.

    Yes there is...
    Conductivity generally refers to the ionic compounds, or salts, dissolved in the water.
    Total hardness is generally the Calcium and Magnesium compounds in solution.
    TDS is the total dissolved solids and includes is all organic and inorganic molecules and elements in the water.

    1oGH = 10mg/l of calcium or magnesium as an oxide.
    Therefore 125.9mg/l of assumed pure Ca would be;
    125.9 / 40 (Molecular weight of Ca) gives 3.1475
    3.1475 x 56 (Molecular weight of CaO) gives 176.26mg/l

    So you would have a GH of 17.6, which as you stated, is what the water company stated. Therefore all your GH seems to be Calcium. You may find you need to add some Mg as lack of this may cause stunting.

    As to the rest I would think that reduced EI dosing would see you fine. I say reduced as you have a fair bit Nitrate in your tap water and may want to dose a little less of this, especially as you seem to plan to have lots of low-growing plants rather than a load of fast growing stems, but there are other on here who can advise you far better on EI dosing than me...
  3. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

    11 Jul 2007
    Chicago, USA
    There is no real conflict between moderately high GH, such as you have, and most plants. There are only a handful of plants that have difficulty growing in high GH (such as Tonina). Avoid these and the rest will do fine. The ads are either propaganda or based on obsolete data.
    Normally it pays only to start the ground cover plants like HC/Glosso emersed due to the problems with algae and CO2 demand. The other items on the list are not worth the trouble as they adapt quite easily to submersion. Just start the ground cover emersed and get the others when you are ready to add water. This makes make life easy because you don't have to worry about their drying out.
    This is also not really worth the trouble and expense unless you have some specific need to lower the TDS for your fish
    Adaptation is the name of the game for aquatic plants (first floods, then drought for example). Most will grow within a wide variety of conditions.
    Check Frolicsome_Flora's magic calculator. It will tell you the dosing scheme for MgSO4.
    You can just use the recommendation on the AE website "1/8 of a teaspoon per 100L. If you notice deficiencies, add more accordingly." I'm not really sure of the relative composition.
    Yes, this will work as well.
    Yes these are all related. TDS=Total Dissolved Solids. The concentration of the dissolved minerals have an effect on the transmission of electricity within the water.
    GH is a measure only of Ca and Mg, therefore is not affected by the addition of KH2PO4 or KNO3. Since these are salts however there will be a rise in TDS and, by definition, conductivity. But once again, so what? This is only an concern if you are breeding soft water fish, or the dozen or so plants in which soft water is mandatory.
    No, this is another myth. Although high General Hardness water also normally has high Carbonate hardness there is no mathematical relationship between the two. Carbonate Hardness is a misnomer and it really should be referred to as Alkalinity as it is a measure of the ability of water to resist acidification due to it's content of Carbonates and Bicarbonates.

    I would not fixated too much on water hardness and Mg as a 17GH water will be OK for maybe 95% of the 300 or so species. Mg is easy to fix with epsom salts. My personal philosophy is to completely ignore the water report when it comes to the nitrate and phosphate content. You will have much bigger headaches with inadvertent macro nutrient deficiencies than with Mg deficiency if you underdose based on your water report.

  4. Hoejay

    Hoejay Member

    29 Oct 2007
    Thankyou for the replies

    Very helpful advice on the water hardness.

    What would you advise on planting density for a carpet of HC or glosso, i intend to more or less to carpet the whole substrate.
    Would say a planting density of 100 - 150 plantlets over my base approx 79x27cm

    I usualy go to my LFS, but choice is limited, having never purchased from one of the online plant suppliers, what would be the ideal way to purchase, by pot or mat or by individual numbers of plantlets. I assume this would be more difficult to request due to the size of the plantlets.

    Could I assume a pot to be about 25 individual plantlets so 5 - 6 pots. Would mats of plantlets be more difficult to seperate or is there no need?

    I assume that with a mat there would initially be a more dense carpet but if left on the mat it would not spread as if planted into the substrate?


  5. Dan Crawford

    Dan Crawford Founder Staff Member

    21 Jun 2007
    Daventry, Northants
    Hi mate, i'm just guessing but are you near Milton Keynes? if so get down to Dobbies garden centre coz they have glosso in pots 3 for £8 and it's in good nick too. They stock the best quality plants i've seen in an LFS and it's all Tropica stock. Far better than getting it of tinternet and we need to encorage shops to stock decent plants. You may wanna call ahead to make sure they have some left.
    With glosso buy as much as you can afford (within reason!) and plant each plantlet singularly about 1cm apart. It takes ages but it's defo the best way. Jeremy's tank in this months PFK was planted this way and it was a full carpet of a 120cm in like 6 weeks.
    I've never planted out of pots really so i can't help you on how many pots to get sorry.



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