Fertilator - my tests show different results on several GH related elements - The Planted Tank Forum
 
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post #1 of 11 (permalink) Old 08-28-2005, 01:22 AM Thread Starter
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Fertilator - my tests show different results on several GH related elements

Has anyone tested out on their own the results that show up on the fertilator? I haven't had any trouble with NO3 or PO4 turnouts, but am not getting the same results when trying (CaSO4)2.H20 (i.e. Gypsum / Plaster of Paris) or MgSO4.7H20 (i.e. Epsom Salt).

I tested out by dosing 1 teaspoon into a 5g bucket. With Gypsum my 2 seperate test results showed a 6.75 dGH (121ppm) increase. While Fertilator shows that it should have yielded a 45ppm (2.5 d) increase to GH. Pretty far off from actuals.

I did the same test with Epsom Salt. Fertilator showed a yield of 25ppm (1.4 dGH), while the actual result was near 6d or 107ppm.

Any idea what could be going on?

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post #2 of 11 (permalink) Old 08-28-2005, 03:20 AM
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The fertilator gives numbers for Ca++ and Mg++, while your GH kit gives you numbers in equivalent CaCO3, to convert:

Ca= CaCO3/2.5
Mg=CaCO3/4.1

Your numbers are actually pretty close.


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post #3 of 11 (permalink) Old 08-28-2005, 03:28 AM Thread Starter
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Thanks for the clarification! Your right, my numbers are near exact to that.

So theoretically I will be getting a false reading from my GH testkits once I start dosing these 2?

My normal GH is 4.75d, and my city report says this is from CaCO3. So at least up to that point I know that the 4.75d is accurate. Anything on top of that I would have to take the difference and divide accordingly, then add back, correct?

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post #4 of 11 (permalink) Old 08-28-2005, 03:35 AM
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well, actually even your city water most likely has both Ca and Mg. Reporting numbers in CaCO3 does NOT mean that the GH is actually from CaCO3 at all, nor does it mean you have no Mg in the tap water! The only way to find out is to buy a separate Ca kit(Lamotte, for example) and use in conjunction with a GH kit, to find out how much of GH is from Ca, how much is from Mg.

To use an analogy, on fertilizor bags, you see numbers for P2O5 and K2O are listed, but that does not mean the actual product has those ingredients at all, more likely they are in the form of PO4 and K+. Those number are given for the equivalent P and K contained in it.


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post #5 of 11 (permalink) Old 08-28-2005, 03:44 AM Thread Starter
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I guess I am still confused then.

Since my testkit says 85ppm GH, is there for sure a combination (regardless of what the % of Ca or % of Mg is) of Ca & Mg equal to 85ppm in the tank, or is it possible that the GH testkit is reading wrong (due to the CaCO3 reading you discussed above), thus making the actual Ca/Mg combo less than 85ppm?

If I wanted to start dosing 36ppm GH, utilizing Gypsum and Epsom Salt, should I just base the dosage amount on what shows up on the Fertilator (already takes into account the divisions of 2.5 and 4.1, for Ca and Mg, respectively), to add up to 36ppm (probably 27ppm Ca and 9ppm Mg)? Thus, totally ignoring the new reading of GH on my testkit, and just knowing that my new GH is 36ppm greater?

Hope this makes sense. I would like to avoid buying a Lamotte Ca testkit. I guess it is not essential anyway.

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post #6 of 11 (permalink) Old 08-28-2005, 10:16 AM
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Quote:
Originally Posted by Spar
... is there for sure a combination (regardless of what the % of Ca or % of Mg is) of Ca & Mg equal to 85ppm in the tank...
In simplified terms, what the reading is telling you is that you have Ca AND/OR Mg to a combined level of 85ppm. Now that could mean that you have 84ppm of Ca and 1 ppm of Mg... or 50ppm of Ca and 35ppm of Mg... or 84ppm of Mg and 1ppm of Ca. Hence the usefulness of knowing how much of that reading is Ca: the remainder can be assumed to be from Mg.

A lot of tap water have these elements in a ratio of around 2-5:1 (Ca to Mg). But where I live most of my GH is made up of Ca (something like a 9:1 ratio). Now with my tap water GH of 18 even at a ratio of 9:1 I have enough of both elements!

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post #7 of 11 (permalink) Old 06-20-2006, 11:00 AM
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My bags of dry ferts display different chemical compounds. Looking this up on past threads I came across this quote by Shalu:

Quote:
Originally Posted by shalu
To use an analogy, on fertilizor bags, you see numbers for P2O5 and K2O are listed, but that does not mean the actual product has those ingredients at all, more likely they are in the form of PO4 and K+. Those number are given for the equivalent P and K contained in it.

Would someone be able to explain this to me, or just confirm that this is true? My Nitrates come from Nitrate of Soda (N), Superphosphate (P2O5), and Muriate of Potash (K2O).

I am asking this because I was reading the dosing threads to learn how much dry ferts to dose in my tank. I was up all night trying to figure out calculations for the chemical compounds in my ferts thinking they were different (P2O5 instead of P2O4 etc), but then I found this thread.
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post #8 of 11 (permalink) Old 06-23-2006, 01:55 PM
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Spar, You can request a "full" water analysis report for the water co. I usually call them and they send it at N/C, and pretty quickly. It should show the levels of Ca, Mg, Mn and a whole lot of others - even B, Mb. Look at that before you start adding things like Ca or Mg. Lots of water supplies have sufficient concentrations of most of the elements already.
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post #9 of 11 (permalink) Old 06-23-2006, 05:34 PM
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Let me add an analogy that might help your understanding:

If I tell you I have three dollars in my pocket, you know I can buy a cheap meal at McDonalds, but you still don't know what combination of coins/paper I'll pull out of my pocket.

The GH test measures the ability of the various ions in the water to react with another chemical (EDTA) - but it does not differentiate between each type of ion. It isn't considered important since the chemical reaction is still in the same ratio (1:1).

Reporting the GH in degrees CaCO3 equivalent is like saying you have the equivalent of three dollar bills in your pocket when you actually have a mixture of quarters, dimes, and nickles. The buying power (performance) is the same - the details are different.

The fertilizer analogy is the same - K2O is a very reactive chemical - you'll never find it in a bag of fertilizer. However, it is the accepted convention for describing the amount of K in the bag. Why not just use the amount of K? Good question!

Now, for plants we might care a little about how much of the GH is due to Mg - so our best option is a calcium measurement followed by a subtraction from total GH.

Clear as mud???

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post #10 of 11 (permalink) Old 06-23-2006, 08:52 PM
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Quote:
Originally Posted by seastar0328
Would someone be able to explain this to me, or just confirm that this is true? My Nitrates come from Nitrate of Soda (N), Superphosphate (P2O5), and Muriate of Potash (K2O).
Seems like I just posted this:
Nitrate of Soda = Sodium Nitrate = NaNO3
Superphosphate = Ca(H2PO4)2
Muriate of Potash = Potassium Chloride = KCl

The NPK on fertilizers represents the relative percentages of N - P - K as if those compounds were present.

You might read this article on K2O Potassium_oxide . As it explains: "Potassium chloride provides less potassium than an equal amount of potassium oxide. Thus, if a fertilizer is 30% potassium chloride by weight, its standard potassium rating, based on potassium oxide, would be only 19%."
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post #11 of 11 (permalink) Old 06-23-2006, 09:47 PM
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Yeah Ransom, you posted that for me in another thread I asked a similar question to after i posted here. Thanks for all of your help!


KevinC...awesome explanation. I had to read it a few times over but I get what you're saying. Great analogy. Thank you for putting that in laymen's terms. :-)
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