Recommended Scale for Micros

Harris Tiu

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Hey All,

Can anyone recommend a weigh scale that is accurate enough that I can make a reasonably sized micronutrient solution?
Right now, I am using the AWS Gemini-20. It says it reads up to 20g in .001g increments. It also says error should be within +/- 0.005g. Is this scale good enough?

Right now, to get myself within about 0.89% error for dosing Molybdenum, I calculate I need to make a 10L solution. I dose 20mL 3x per week in a 400L aquarium.
This is probably going to expire before I use most of it.

When I apply my milligram scale for Molybdenum, Rotala Calculator says I add 0.560g to the 10L, instead I add 0.565g, this brings me to 0.89% error.
In contrast, If I should add 0.056g to 1L, instead I add 0.061g, this brings me within 8.93% error
 
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Allwissend

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Good enough for hobby grade solutions, do a 100x stock solution. (5.6g in a 1L per your example). Then do a serial dilution to make your final micro solution. Do it with boiled and cooled distilled water and keep it in the refrigerator ... should be good for a long time.

IF, and that's a big if, the error report on the scale is accurate the difference in the final aquarium dose would be around 0.0001 mg/L (0.089 * 0.0011). With the EI approach, this error is not much and about the same as dosing +/- 2mL in your dose.

There are more accurate and better(?) scales there but come at a cost $$$$
 

Harris Tiu

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Good enough for hobby grade solutions, do a 100x stock solution. (5.6g in a 1L per your example). Then do a serial dilution to make your final micro solution. Do it with boiled and cooled distilled water and keep it in the refrigerator ... should be good for a long time.

IF, and that's a big if, the error report on the scale is accurate the difference in the final aquarium dose would be around 0.0001 mg/L (0.089 * 0.0011). With the EI approach, this error is not much and about the same as dosing +/- 2mL in your dose.

There are more accurate and better(?) scales there but come at a cost $$$$
Allwissend,

Thanks for replying. Heres what I gather from your response.

Based on PPM values, you are saying +/- 10% error in dosing is quite acceptable.
So if im dosing 20mL, that error is like adding +/- 2mL. It is like dosing between 18-22mL.
However, if we take the lower part of the error range, its comes to 18mL dosing. Is this a deficit?
Would it be wise to deliberately dose 22mL instead? that way the dose range comes to 20-24mL, possibly + 20% error on the high side, and thus ensuring that we have no deficits?
or does the standard EI approach already take care of that? thus dosing 20-24mL becomes overkill?
 
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Allwissend

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You misread the numbers from my scale and calculations.
Where exactly ?

If I should add 0.056g to 1L,
My suggestion is to make 100x stock solution...100 *0.056= 5.6g in 1L then do serial dilution to your target concentration. This avoids having to make a large volume of solution at one time while keeping the impact of the claimed measurement error to 0.089%. Your scale is suitable.


Next, 10% error in dosing is quite acceptable?
Acceptable or unacceptable is up to you and the task at hand. Percentages always apply to a base number, that's an important part when evaluating their impact. Is adding more or less molybdenum by 0.0001mg/L acceptable? Experience says plants won't care that much if it's 0.001, 0.0011 or 0.0012.
If we apply the 10% error to a larger number, like the weekly dose of a macronutrient such as nitrate, 18 mg/L NO3 (-10%), 20 mg/L (base) or 22 mg/L (+10%), would that be a relevant difference in plant growth to the hobbyist? Compared to the uncertainty of what comes from fish waste, substrate, aquarium volume and tap, I would say it's good enough.
 

Harris Tiu

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Where exactly ?


My suggestion is to make 100x stock solution...100 *0.056= 5.6g in 1L then do serial dilution to your target concentration. This avoids having to make a large volume of solution at one time while keeping the impact of the claimed measurement error to 0.089%. Your scale is suitable.



Acceptable or unacceptable is up to you and the task at hand. Percentages always apply to a base number, that's an important part when evaluating their impact. Is adding more or less molybdenum by 0.0001mg/L acceptable? Experience says plants won't care that much if it's 0.001, 0.0011 or 0.0012.
If we apply the 10% error to a larger number, like the weekly dose of a macronutrient such as nitrate, 18 mg/L NO3 (-10%), 20 mg/L (base) or 22 mg/L (+10%), would that be a relevant difference in plant growth to the hobbyist? Compared to the uncertainty of what comes from fish waste, substrate, aquarium volume and tap, I would say it's good enough.

Allwissend,

So very sorry, I'm the one that misread your numbers.

You were saying +/- 10% error in dosing is not much, quite acceptable.
Would the lower end of the dosage be a deficit?
If the dose was 20mL, would it be wise to deliberately dose 22mL instead, making the dose range between to 20-24mL, possibly + 20% error on the high side, and thus ensuring that we have no deficits?
or does the standard EI approach already take care of that? thus dosing 20-24mL becomes overkill?

Currently looking into this serial dilution method...
 

Allwissend

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It is highly unlikely a deficiency will occur, the recommended EI dose will already provide more nutrients than plants use in that amount of time. That's the benefit of this approach .
 

Harris Tiu

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It is highly unlikely a deficiency will occur, the recommended EI dose will already provide more nutrients than plants use in that amount of time. That's the benefit of this approach .

How long before the 100X stock solution expires?

I think I understand how to perform serial dilution now.
Just talking about Molybdenum for now to isolate variables.

1) Make Acidified Distilled Water by mixing 0.5g of ascorbic acid per 500mL distilled water.
2) Mix 5.6g Molybdenum Crystals (Na2MoO4.2H20) in 100mL of Acidified Distilled Water.
3) Take 1mL of 100x Molybdenum Solution, then add to a 999mL of Acidified Distilled Water. This comes to 1000mL of final solution containing 0.056g of Molybdenum. 20mL of this should produce 0.0011PPM in a 400L tank.

Thank You:)
 

Allwissend

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How long before the 100X stock solution expires?
If it's just the molybdenum solution with distilled water it can be kept for a long time, especially if kept in the fridge (around 4 °C). If you see precipitate or mold growing it's probably time to make another solution.
Mix 5.6g Molybdenum Crystals (Na2MoO4.2H20) in 100mL of Acidified Distilled Water.

Technically that is is 1000x solution, but you also did 1:1000 dilution (1ml in 999mL) so the concentration checks out. It's usually good practice to do a series of 1:10 dilutions rather than one big step.

Looking forward to see your tank.
 

Zeus

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We have taken care of a serial dilutions for trace DIY ferts which may make life a little easier in the IFC Aquarium Calculator

1630133178004.png


Will work for target ppm or from grams, plus covers most salts used and you can compare the ppms of many trace solutions.

May be worth a look ;)
 
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