Calculating Nutrient PPM via Label Ratios ie. Cal Mag

rosecitypapa

rosecitypapa

Active Member
Even wonder exactly how much nutrient you are actually supplying your plants? I do! After talking with two different nutrient manufacturers and getting two different results, I'm still confused.

Here's a quart bottle of Botanicare's Cal-Mag product. On the back label it has:
http://botanicare.net/supplements/cal-mag

2.0 % - Nitrate N
3.2 % - Ca
1.2 % - Mag
0.2 % - Iron

So first convert to mass weight:
at 3.2 % Ca, that is equivalent to 3.2 g per 100 g H2O

Then Convert to ppms:
3.2 g x 10,000 / 100 g x 10,000 =
32,000 g Ca / 1,000,000 g H2O =
32,000 ppm in concentrate

Then Factor in dilution:
1 tsp = 5 ml = 5 g
1 gal H2O = 3785.4 cc's = 3785.4 g H2O
3785.4 g H2O / 5 g = 757 / 1 Dilution

Therefore:

3.2 % Ca = 32,000 ppm / 757 = 42.3 ppm of Ca per 1 tsp of concentrate diluted in 1 gal of H2O

1.2 % Mag = 12,000 / 757 = 16 ppm of Mag per 1 tsp of concentrate diluted in 1 gal of H2O

2% N = 20.000 / 757 = 26 ppm of Nitrogen (Nitrate) per 1 tsp of concentrate diluted in 1 gal of H2O

Total contribution = 84 ppms


However, the other way dilution was calculated was using a dilution factor based on 5 ml / 1000 ml = .005.

Therefore:

3.2 % Ca = 32,000 ppm in concentrate * .005 = 160 ppm of Ca per rate of 1 tsp / gal.

1.2 % Mag = 12,000 * .005 = 60 ppm of Mag per 1 tsp of concentrate diluted in 1 gal of H2O

2% N = 20.000 * .005 = 100 ppm of Nitrogen (Nitrate) per 1 tsp of concentrate diluted in 1 gal of H2O

Total contribution = 320 ppm


Why are the two numbers so off?
I should be able to get to the same ppm per tsp of concentrate, yes?
 
aeviaanah

aeviaanah

Well-Known Member
I think the 1000 dilution rate may just be an estimate for doing 'in brain math'

id take the tsp to gallon being these are the volumes you are working with...

ill stick around to see if someone knows, ive been wanting to know this.
 
rosecitypapa

rosecitypapa

Active Member
aeviaanah, I think you might be right but it's all suppose to work out!

To verify, I started with 1 gal H2O starting at 23 ppm's from my tap. Added 1 tsp/ gal of Cal-Mag and my tds when to 220 ppm. So it seems the Cal-Mag contributed 197 ppms.

Whichi is inconviently neither of my two theoretical numbers.,... ugh!
 
rosecitypapa

rosecitypapa

Active Member
So I found a useful link with examples and exercies:
http://www.greenhouse.cornell.edu/crops/factsheets/FertilizerCalculations.pdf

Their formula is a bit different:

ppm = oz fert per gal of irrigatiton water X 75 (ppm of any soluble in 1 oz of water) X 100 X df
where df equals a dilution factor

so to use Cal Mag

ppm = .169 (oz per 5ml) X 75 X 100 X .032
= 40.56 ppm Ca where Ca is 3.2% and 5ml (1 tsp) is the dilution rate


This seems to correlate with the first example in the original post.

the other values would be:

ppm of mag = .169 x 75 x 100 x .012
= 15.21 ppm Mag

ppm of N = .169 x 75 x 100 x .02
= 25.4 ppm N

Ok, I'm feeling better about the math but I still don't understand why the big variation between these calculated figures and my actual tds reading.
 
aeviaanah

aeviaanah

Well-Known Member
rosecitypapa said:
So I found a useful link with examples and exercies:
http://www.greenhouse.cornell.edu/crops/factsheets/FertilizerCalculations.pdf

Their formula is a bit different:

ppm = oz fert per gal of irrigatiton water X 75 (ppm of any soluble in 1 oz of water) X 100 X df
where df equals a dilution factor

so to use Cal Mag

ppm = .169 (oz per 5ml) X 75 X 100 X .032
= 40.56 ppm Ca where Ca is 3.2% and 5ml (1 tsp) is the dilution rate


This seems to correlate with the first example in the original post.

the other values would be:

ppm of mag = .169 x 75 x 100 x .012
= 15.21 ppm Mag

ppm of N = .169 x 75 x 100 x .02
= 25.4 ppm N

Ok, I'm feeling better about the math but I still don't understand why the big variation between these calculated figures and my actual tds reading.
Click to expand...
nice find bro! possibly there is some inactive ingredients in calmag? i use calmag plus...is this what you are using?
 
acellular

acellular

Member
I calibrated my ppm and p.h. meter today and did a test on 0ppm r.o. water and got:
Fulvex at 3ml./gal. = 40ppm
CalMag+ at 3ml./gl. = 135ppm.
Fuvex and CalMag+ at 3 ml./gallon each = 175ppm
P.H. at 4.5 after adding Fulvex and CalMag+
6 drops of P.H. up from Botanicare brought P.H. to 7.2
PPM went from 175 to 183 after adding P.H. up.
 
B

bigbong1411

Well-Known Member
rosecitypapa said:
Even wonder exactly how much nutrient you are actually supplying your plants? I do! After talking with two different nutrient manufacturers and getting two different results, I'm still confused.

Here's a quart bottle of Botanicare's Cal-Mag product. On the back label it has:
http://botanicare.net/supplements/cal-mag

2.0 % - Nitrate N
3.2 % - Ca
1.2 % - Mag
0.2 % - Iron

So first convert to mass weight:
at 3.2 % Ca, that is equivalent to 3.2 g per 100 g H2O

Then Convert to ppms:
3.2 g x 10,000 / 100 g x 10,000 =
32,000 g Ca / 1,000,000 g H2O =
32,000 ppm in concentrate

Then Factor in dilution:
1 tsp = 5 ml = 5 g
1 gal H2O = 3785.4 cc's = 3785.4 g H2O
3785.4 g H2O / 5 g = 757 / 1 Dilution

Therefore:

3.2 % Ca = 32,000 ppm / 757 = 42.3 ppm of Ca per 1 tsp of concentrate diluted in 1 gal of H2O

1.2 % Mag = 12,000 / 757 = 16 ppm of Mag per 1 tsp of concentrate diluted in 1 gal of H2O

2% N = 20.000 / 757 = 26 ppm of Nitrogen (Nitrate) per 1 tsp of concentrate diluted in 1 gal of H2O

Total contribution = 84 ppms


However, the other way dilution was calculated was using a dilution factor based on 5 ml / 1000 ml = .005.

Therefore:

3.2 % Ca = 32,000 ppm in concentrate * .005 = 160 ppm of Ca per rate of 1 tsp / gal.

1.2 % Mag = 12,000 * .005 = 60 ppm of Mag per 1 tsp of concentrate diluted in 1 gal of H2O

2% N = 20.000 * .005 = 100 ppm of Nitrogen (Nitrate) per 1 tsp of concentrate diluted in 1 gal of H2O

Total contribution = 320 ppm


Why are the two numbers so off?
I should be able to get to the same ppm per tsp of concentrate, yes?
Click to expand...

You just made a silly mistake with your second dilution. You should have done 5ml/3785.41ml and not 5ml/1000ml.

The Cal-Mag Plus that I have lists:
N=2.0%
Ca=3.2%
Mg=1.2%
Fe=0.1%

At 5ml/gal I got a ppm of 248. However, I used a pyrex measuring cup and only used 500ml so that wasn't super accurate. I do have a pipette and added 660uL Cal-Mag Plus.

500ml/3785.41 = 0.132086

0.132086 x 5ml = 0.66043ml or 660uL Cal-Mag Plus

*Edit* I just saw that someone already answered that question... and I'm about three years late as well ;)
 
C

churchhaze

Well-Known Member
rosecitypapa said:
at 3.2 % Ca, that is equivalent to 3.2 g per 100 g H2O
Click to expand...
3.2% Ca means 3.2g per 100g of the total mixture mixture, which includes the Ca and other elements.

It is not 3.2g Ca per 100g of just water alone. Water has a different density than the complete mixture, and that needs to be taken into account when converting to volume.

rosecitypapa said:
Then Factor in dilution:
1 tsp = 5 ml = 5 g
Click to expand...
This is where you start to see the problem. 5mL of solution doesn't equal 5g. That would only be true if the mixture was water, which is not possible if 3.2% of that mixture by mass is calcium. You need to know the density of the mixture in this case. Really, the best way to find this is just to measure the mass of a constant volume of the mixture.
 
C

churchhaze

Well-Known Member
For the record, the ppm reading on ppm/EC meters is not accurate readings of ppm (mg/L) of total dissolved solids, but just an estimate based on EC. Different ions affect EC differently, and pH also plays a large role as OH- and H3O+ ions also have a big effect on EC.

Also, don't buy cal-mag$
 
You must log in or register to reply here.
Top