Good scale to weigh g and mg ferts? - The Planted Tank Forum
 
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post #1 of 13 (permalink) Old 10-18-2015, 04:50 PM Thread Starter
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Good scale to weigh g and mg ferts?

Looking for a digital scale that can handle milligram through gram accurate weighing without costing a fortune. Any recommendations based on your experiences with specific products would be appreciated.

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post #2 of 13 (permalink) Old 10-18-2015, 05:56 PM
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I use a Gemini 20 scale. Cheap $20 scale but has been very accurate for going on 3 years now. It's accuracy is within 1mg which is far more than we need.

The only problem I have with it is the size of the tray. When I need to weigh more than the tray accepts I set a small styrofoam cup (or anything very light) on the tray and tare it to zero.

We really don't need high priced scales for fertilizers IMO.

Here is a comparison of this cheap scale against an expensive one. The cheap little guy wins lol.

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post #3 of 13 (permalink) Old 10-18-2015, 06:12 PM
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Quote:
Originally Posted by AquaAurora View Post
Looking for a digital scale that can handle milligram through gram accurate weighing without costing a fortune. Any recommendations based on your experiences with specific products would be appreciated.
Like Zorfox I just bought a $20 jewelers scale, got mine off of fleabay


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post #4 of 13 (permalink) Old 10-18-2015, 06:38 PM
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+1 for the cheapo scale...e-bay $12 for mine. Same small tray size issue/w same fix.

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post #5 of 13 (permalink) Old 10-18-2015, 06:45 PM
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I will add that I stopped weighing my ferts shortly after starting, I just use a 1/4tsp (N,P,K) a 1/8tsp (CSM+B & Iron), and a 1tsp (GH booster & Declor) measuring spoons, scoop and dump. Got real tired real fast of having to sit down every week/every other week and weigh ferts, I'm just that lazy


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post #6 of 13 (permalink) Old 10-18-2015, 07:17 PM
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I will add that I stopped weighing my ferts shortly after starting,...Got real tired real fast of having to sit down every week/every other week and weigh ferts, I'm just that lazy
Agreed. I did the same thing. Dry dosing with teaspoons is fine for 30 gallons or more and solutions for the smaller ones. Teaspoons are close enough for fertilizers IMO. No need to hit the bullseye as long as you hit the dart board.
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post #7 of 13 (permalink) Old 10-18-2015, 09:14 PM Thread Starter
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Thank you for the input thus far everyone! Raymond what brad (name) is your scale?
Happy to hear from others what scales they did and/or did not like (mainly accuracy).

I wanted something to get initial weight down for ferts, and also to use for weighing out potassium permanganate (10mg per 0.3g) for plant dips. The smallest amount of PP i can buy is 1 ounce..I'd used 0.001 ounce=30 mg for a 1g dip (roughly).. kinda hard to separate the granules by hand enough to get to that small a portion without a scale.

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post #8 of 13 (permalink) Old 10-25-2015, 07:05 PM
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Is there a conversion for weight of ferts per gallon of water in the column?


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post #9 of 13 (permalink) Old 10-26-2015, 12:04 AM
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Originally Posted by Tihsho View Post
Is there a conversion for weight of ferts per gallon of water in the column?
I'm not sure I understand your question. Do you mean mg per gallon?

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post #10 of 13 (permalink) Old 10-26-2015, 12:24 AM
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Exactly that. I know before it was based by teaspoons, but for automation purposes I want to go with a mg per gallon option.


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post #11 of 13 (permalink) Old 10-26-2015, 01:59 AM
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Actually, the teaspoon measures are not nearly as accurate. That said fertilizers are like hand grenades. All you need to do is get in the ball park.

There is quite a bit of math to do what you want. It's easier to use a nutrient calculator. If you want to use one you can use this online version or download my Windows version.

I'm adding how to do them manually just in case you or others would like to know. There are various formulas depending on the measures but this is the basic math to accomplish this.

Parts per million is one milligram per liter. So if you add say one mg of Potassium to one liter you have 1ppm of Potassium.

Here's the problem. Our fertilizers are not elements like potassium. Instead, they're a mixture of elements or molecules.

Take K2SO4 for example. It has 3 elements. So wee need to know the percentages of each. I won't explain how to calculate that. Instead you can use a molar mass calculator to see the numbers.

If you enter K2SO4 in that calculator you will see we have the following,

Code:
Symbol	Element		Atomic weight	Atoms	Mass percent
K	Potassium	39.0983		2	44.8737 %
S	Sulfur		32.065		1	18.4008 %
O	Oxygen		15.9994		4	36.7255 %
Potassium is 44.87% of K2SO4. That means that 1mg of K2SO4 has 0.4487mg of potassium (move the decimal to the left two places).

That's all we need to make a calculation.

Example, We want 15ppm of potassium in 10 gallons.

First convert gallons to liters,

10 * 3.78541 = 37.8541 liters

Remember K2SO4 has 0.4487mg of potassium per miligram so,

15 / 0.4487 = 33.43

So we need to add 33.43mg to one liter of water to get 15ppm

10 gallons has 37.8541 liters so,

37.8541 * 33.43 = 1,265.5 mg

So we need to add 1,265mg to 10 gallons to increas K to 15ppm.

It's also necessary to convert forms of nutrients. In this hobby we use NO3 as nitrogen and PO4 as phosphorus. So we need to remember to convert those numbers. There are tons of conversion charts available.

Example, if you want 7ppm of NO3 you need to convert to nitrogen. The conversion factor is 0.22.

So 7(NO3) * 0.22 = 1.54(N)
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post #12 of 13 (permalink) Old 10-26-2015, 02:46 AM
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I thought this was kinda cool.
http://www.amazon.com/Digital-Measuring-Spoon-Accurate-Measurements/dp/B00WYDP66E/ref=sr_1_5?ie=UTF8&qid=1445823902&sr=8-5&keywords=scale+spoon


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post #13 of 13 (permalink) Old 10-26-2015, 02:55 AM
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Seachem also has one of these. I'm not sure I want to put pressure on a sensor scooping things out and expecting it to hold a zero then giving me a weight. I'd rather tare a scale and add a mass to it and go from there.


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