# Mg Density input needed



## BryceM (Nov 6, 2005)

It looks like we might be able to update the Fertilator soon.

One thing that we need help with is determining the density of a typical teaspoon of dry MgSO4.

To do this correctly, please weigh a level teaspoon of your particular dry MgSO4 powder/pellets/etc.

Post the answer here, along with the type and source of your ferts (pellets / Greg Watson, powdered Walmart Epsom Salts, etc.).

I'm hoping to get responses from 10 or 20 people to get a reasonable consensus. FYI the correct answer should be in the neighborhood of 4 or 5 grams/tsp. One or two decimal point accuracy would be nice.

- GB


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## Left C (Jun 14, 2005)

Hi guaiac_boy

Are you asking for the weight of Magnesium Sulfate (MgSO4) or Magnesium Sulfate Heptahydrate (MgSO4∙7H2O) - Epsom Salt? 

My scales only weigh to one decimal place. The following are the results of weighing 20 tsp of Magnesium Sulfate Heptahydrate (MgSO4∙7H2O). The plot is a histogram and you can see how variable the weight of this compound can be. My box of Epsom Salts varies from a powder to crystals.

The average is: 6.465 grams per teaspoon or 6.5 grams per teaspoon

5.9 x 
6.0 
6.1 xxxx
6.2 xx 
6.3 xxx 
6.4 x 
6.5 xx
6.6 xxx 
6.7 
6.8 
6.9 x
7.0
7.1 x
7.2 x
7.3 x

I hope this helps you with the fertilator.
Left C


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## BryceM (Nov 6, 2005)

Well, any MgSO4 that has had contact with the atmosphere will be at least partially hydrated. My understanding is that almost all of what gets used for aquarium use is MgSO4-7H2O. Am I certain about that? No, probably not.

Thanks for the input.


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## Left C (Jun 14, 2005)

guaiac_boy said:


> Well, any MgSO4 that has had contact with the atmosphere will be at least partially hydrated.


Pure MgSO4 hydrates very, very easily and it is very hard to work with when you want to weigh it out correctly.

Many people refer to Magnesium Sulfate Heptahydrate as Magnesium Sulfate. It can get confusing even though they are different compounds.

You want to make sure that the Mg calculations are correct. Let me show you:

MgSO4∙7H2O is 246.3 AMU and it contains 9.9% Mg.
MgSO4 is 120.3 AMU and it contains 20.2% Mg.



guaiac_boy said:


> My understanding is that almost all of what gets used for aquarium use is MgSO4-7H2O. Am I certain about that? No, probably not.


That's correct as far as I know.



guaiac_boy said:


> Thanks for the input.


You're very welcome. I'm not trying to throw a monkey wrench or anything like that. I'm trying to help. I'd like for the fertilator to get fixed. It can be a very useful tool with a bit of tweaking.


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## JamesC (Jul 26, 2005)

I get my MgSO4∙7H2O from Aqua Essentials in the UK and is crystalline in form. Using a standard teaspoon (5ml) I get and average weight of 5.1g using a calibrated balance accurate to 0.1g.

Just noticed there is an error in the Fertilator under conversion of tbs / tsp ........
MgSO4∙7H2O is 12.00g for a tbs and 14.00g for a tsp. Shouldn't it be 4.00g for a tsp?


HTH
James


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## tropism (Jul 21, 2006)

James,
Yeah, that's a typo. The values for MgSO4.7H2O listed in that "Conversion of tbs / tsp / ... / gram" table are based on 4 grams per teaspoon (except for the '14.00'). The thing is, even the "corrected" value 4.00 seems pretty low considering what most people are reporting for their measurements.

For what it's worth, that table isn't actually used internally by the Fertilator for any calculations. But... the values shown should at least be consistent with what *is* used for the calculations. So I guess the question is: _Do we just update the values shown in the table to match the conversion factor that's used by the Fertilator for calculations (4.844 g/tsp), or can we decide on a "better" number and update both what's shown in the conversion table AND what's used for calculations_? (Heh, don't worry about whether we can get someone to do it or not... I'm the one currently working on the Fertilator bug fixes, and I can change both of those things pretty easily. )

I don't have time right now, but later today I'll post some measurements I made for MgSO4.7H20 grams per teaspoon.


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## BryceM (Nov 6, 2005)

OK everyone. Help is still needed with this. I'll be posting my results tomorrow. It'd be nice to get info from at least 6 people.


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## Brilliant (Jun 25, 2006)

Hmmm I have lots of Magnesium Sulfate from www.GregWatson.com around because I thought I needed it for a planted tank 

Here is what my Ohaus CS-200 says for 1 teaspoon...

4.6g
4.4g
4.7g
4.8g
4.7g

Mine is also in powder and crystal form I wonder why its so different.


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## tropism (Jul 21, 2006)

Left C, I'm pretty surprised by how high your average was, even if you don't consider the stragglers above 6.6 -- I'm not saying (or even implying) that your measurements weren't "correct", I just wasn't expecting that. 
---

I tried with 3 different sets of measuring spoons and two "different kinds" of MgSO4.7H20. One was from Greg Watson a couple years ago and was mostly powdery/small crystals, the other was from a local grocery store (H.E.B. brand -- it's mainly a Texas thing) that had mostly bigger crystals. I used a calibrated scale that's accurate to +/-0.01 grams.

Here are my numbers:

Greg Watson's
tsp A - 4.06, 4.23, 4.20, 4.30, 4.23 : *average 4.20*
tsp B - 5.35, 5.30, 5.25, 5.33, 5.37 : *average 5.32*
tsp C - 5.28, 5.22, 5.32, 5.36, 5.22 : *average 5.28*​HEB brand
tsp A - 4.37, 4.41, 4.33, 4.32, 4.31 : *average 4.35*
tsp B - 5.28, 5.36, 5.33, 5.36, 5.38 : *average 5.34*
tsp C - 5.24, 5.25, 5.15, 5.21, 5.11 : *average 5.20*​
So, even with the same scale and same batches of MgSO4.7H2O, it's definitely possible for different measuring spoons to be off by more than 1 full gram.


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## Left C (Jun 14, 2005)

tropism said:


> Left C, I'm pretty surprised by how high your average was, even if you don't consider the stragglers above 6.6 -- I'm not saying (or even implying) that your measurements weren't "correct", I just wasn't expecting that.
> ---
> 
> I tried with 3 different sets of measuring spoons and two "different kinds" of MgSO4.7H20. One was from Greg Watson a couple years ago and was mostly powdery/small crystals, the other was from a local grocery store (H.E.B. brand -- it's mainly a Texas thing) that had mostly bigger crystals. I used a calibrated scale that's accurate to +/-0.01 grams.
> ...


Hi tropism.

I just used two different measuring spoons too see what the difference could be. It agrees with what your are saying about the differences in the spoon size can possibly be off by more than one gram.

I used a stainless steel 5 mL or 1 tsp measuring spoon called Spoon B. Spoon B held 5.2 mL of water. The other measuring spoon is made of plastic called Spoon C and it held 4.5 mL of water. A 0.7 mL of water volume is a significant difference.

My digital scales came from AquaticEco.com. It's their Sper Scientific Pocket Balance 100006. They measure to one decimal place. I calibrated them with the 100 gram weight before use. I used a weight boat to hold my sample. The weight boat had a tare weight of 2.5 grams that was zeroed out. I used a fresh sample for each test and I pored what I just weighed into a different container.

My MgSO4∙7H2O came from a local pharmacy that I've had for over a year. It's powdery and it has crystals too.

I weighed 20 one tsp samples of each teaspoon. Here are the results:

Spoon B - Stainless Steel 
5.7 x
5.8 xx
5.9 xxxxxxx
6.0 xxx
6.1 xxxxx
6.2 
6.3 xx
Average = 6.0 grams

Spoon C - Plastic 
4.5 xxxx
4.6 xxx
4.7 xxxx
4.8 xxxxx
4.9 xxxx
Average = 4.7 grams

This agrees with what you are saying about the variances between measuring spoons.

Left C


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## tropism (Jul 21, 2006)

Wow, thanks, Left C! Above and beyond the call of duty 

I'd also like to say thanks to everyone that's responded, and a "thanks in advance" to anyone else who responds. Even if you don't have time (or just don't feel like) measuring out 20 teaspoons, all measurements are greatly appreciated! The more people (or different teaspoons) we get input from, the more likely we are to come up with a number that's at least close for the majority.


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## BryceM (Nov 6, 2005)

I never thought there would be so much variation between "teaspoons". Great.

Now we have one equation with two unknowns.........

Oh well. Carry on. More data please....


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## Squawkbert (Jan 3, 2007)

guaiac_boy said:


> I never thought there would be so much variation between "teaspoons". Great.


All the more reason to do everything by weight.


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## Left C (Jun 14, 2005)

tropism said:


> Wow, thanks, Left C! Above and beyond the call of duty
> 
> I'd also like to say thanks to everyone that's responded, and a "thanks in advance" to anyone else who responds. Even if you don't have time (or just don't feel like) measuring out 20 teaspoons, all measurements are greatly appreciated! The more people (or different teaspoons) we get input from, the more likely we are to come up with a number that's at least close for the majority.


I'm very glad to help out.

I never thought about measuring the volume of a measuring teaspoon by using water until you mentioned the variation of your different spoons. I did ass-u-me that each of my measuing teaspoons should be close to 5 mL, but they aren't. It is a real eyeopener for me.


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## Brilliant (Jun 25, 2006)

I don't think everyone's got an accurate scale. I really think the fertilator could use some help.

Well that caught my interest and I just so happen to have another spoon marked 1 tsp - 5ml so here goes.

5.2g
5.1g
5.4g
5.3g
5.4g


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## Edward (May 25, 2004)

If someone could just remove the extra number *1 *on the front of the *4.00* TSP 1 tsp 5ml for MgSO4.7H2O then we are done.


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## BryceM (Nov 6, 2005)

Yes Edward, that would help, but from the data above 4.00g/tsp doesn't seem to be all that acurate either.


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