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Nutri-Calc & MgSO4

Discussion in 'Advanced Strategies and Fertilization' started by EssexPete, Aug 18, 2006.

  1. EssexPete

    EssexPete Prolific Poster

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    Nutri-Calc indicates 3 1/8 tsp MgSO4 3 times a week for my 77 (UK) gall tank which seems quite a lot - I'm sure it would have a devastating effect on me :D
    I have dosed it at this rate for the last week and the plants have definately improved in growth and appearance, however I have also noted that new leaves on my HYGROPHILA are very curved-in on the sides - is it likely that the MgSO4 dosing is causing this.
    All the other plants seem fine.

    The other point I've noted is that cabomba has taken-off like crazy since switching to EI. I have to trim about 6" from each plant every day, mainly because the internode distance is now about 6"

    I've been a convert to Tom's EI dosing since 1/8/06
    100 UK gall tank - approx 77 galls H2O
    3 x 36w triton tubes - 12 hrs/day
    2 x 150w metal halide lamps - 9hrs/day
    Eheim 2329 wet/dry (bio) filter
    Eheim 2217
    Pressurised CO2 when the MH lamps are on (around 10 bubbles/sec (?)too fast to tell really)
    pH of outgassed tank water ~7.6
    pH before CO2 switches on ~7.1
    pH at lights out ~6.4
    (pH values from pH controller)

    Thanks
    Pete
    CO2 photo diary at - http://uk.pg.photos.yahoo.com/ph/speedy99uk/my_photos
     
  2. quenton

    quenton Guru Class Expert

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    Re: Nutri-Calc & MgSO4

    Yes, Mg and Ca take large quantities to get a reasonable ppm. However, your source water may well have quite a bit of either or both.

    My source water (according to the city "experts") comes in at 8ppm, and my default target for Mg is 10ppm.

    For my 77g :) (I don't really have one, but my 65g + my 29g after reductions to get actual water just happens to come to 77g US) gets 1/2tsp MgSO4 to bring it up to the 10ppm.

    Getting the water specs seemed a bit of a trial until I told the person on the phone that I kept aquariums and he said "Oh, OK, I'll email you the report".
    I don't know why that was magic, maybe he thought I was an environmentalist and wanted ammunition to scream at the water dept :D
     
  3. Tom Barr

    Tom Barr Founder
    Staff Member Administrator

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    Re: Nutri-Calc & MgSO4

    Just tell them you are a horticulturist and need to know for fertilization for plants. Act like Farmer Bob.
    You basically are anyway.

    That throws them off the scent.
    Some depts don't have chem folks and they send out their lab stuff for the other things, like Mg, Ca, and other nutrients to independent contractors.
    So the person you get on the phone is often not aware of the process, what's going on etc.
    They want to help, but their main focus is providing potable drinking water, not chemical nutrient anaylsis for planted tanks.
    Some things they can tell you, namely NO3 levels.


    Regards,
    Tom Barr
     
  4. EssexPete

    EssexPete Prolific Poster

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    Re: Nutri-Calc & MgSO4

    Thanks Quenton

    You say that you use 1/2 tsp to bring your Mg level up in 77 galls, yet NutriCalc indicates a little over 3tsp 3x per week for my tank.

    As you suggest, it seems I have VERY little CO2 in my tap water, in fact it seems I have a negative amount of MgSO4!

    Mg testing
    ((17.86 x dGH) - (2.5 x Ca ppm)) / 4.1 = Mg ppm

    Using this formula I get the following -

    ((17.86 x 13) - (2.5 x 95)) / 4.1 =
    (232 - 237.5) / 4.1 = -1.34

    Hmmm - so I have -1.34 ppm Mg/l :confused:

    The dGH and Ca ppm were derived from the Nutrafin test kits and these results have been stable over several weeks.

    Here's the word for word instructions from the Nutrafin tests for Ca -
    (NB - I used 5 drops of reagent 3)

    CALCIUM ANALYSIS VERSUS GENERAL HARDNESS ANALYSIS

    Ca2+ mg/L (ppm)
    Multiply the total number of drops of reagent #3 used by 20 to determine the Calcium concentration.
    To determine the ratio between Calcium & Magnesium
    1. Calcium mg/L (Ca2+) (multiply by) x2.5 = Calcium Hardness mg/L (CaCO3)
    2. General Hardness mg/L (CaCO3) (minus) - Calcium Hardness mg/L (CaCO3) = Magnesium Hardness (CaCO3)
    3. Magnesium Hardness (CaCO3) (divided by) / 4.1 = Magnesium mg/L Mg2+

    Thanks
    Pete
     
  5. quenton

    quenton Guru Class Expert

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    Re: Nutri-Calc & MgSO4

    It takes 1/2tsp of MgSO4 for my 77g because it starts off at 8ppm, so I only need to add 2ppm to get to my desired 10ppm.

    The formula for calculating Mg based on kh and Ca can result in just about anything you want with a very small difference in one of the readings -- so small that its well within the test kit accuracy. I stopped trying to measure it many months ago and I just go by my source water test.

    As you noted, the test and calculation indicates a -ve amount -- so you really have to ignore it. If you cannot get source water specs, or if you doubt them, Mg and Ca don't go away so you can find a lab that will test it.
     
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