Backyard Aquaponics
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Ok not the hairy creatures that do so much damage to a lawn,but molecular weights of chemicals.Ok i want a ratio of 2-1-.5 between three chemicals,for this example Potassium sulphate,Calcium carbonate and Magnesium sulphate,so the information i have is Potassium sulphate is 50% Potassium and i know the molecular weight of all three.
So if i want a 200 ppm level of Potassium,it goes 200/0.5/1000,which gives me 0.4 mlg per litre to achieve 200ppm.
The molecular weight of Potassium sulphate is 174.2592,Calcium Carbonate is 100.0869 and Magnesium sulphate is 120.366.
So how do work out a 2-1-.5 ratio from these figures ? if its easy please dont laugh..

So is what you're really asking for a ratio of 2 - 1 - 0.5 for Potassium, Calcium and Magnesium or do you actually want it for Potassium sulphate,Calcium carbonate and Magnesium sulphate?

What I'm thinking you're asking is to find the amount of each chemical to give you a ratio of 2 to 1 to 0.5 for Potassium to Calcium to Magnesium, is this right?

I just work off the amount of finished spray I'm making up, and then start with the "1".

ie: I oz of Calcium, 2 oz. of Potassium, and 1/2 oz. Magnesium.
I've always used volume as opposed to weight. If the label only gives weight and not volume, I'll weigh the chemical out to get the volume to use, then mark that on the bottle for future reference. Most of my lawn chemicals are in volume, not weight, and come with measuring devices if they are very low use products. Some of the newer product are 2 acres per 1.3 oz, so mixing small quantities you use very small amounts of product.

Using your formula, I use the above when my PH drop below 6.4.

I used those three as an example as i have been trying to work out the correct weights for nutrients,in hydroponics if you mix your own nutrients you have to b fairly accurate with the measures of each nutrient,I have always thought of dosing with Potassium sulphate at 1 teaspoon per 1000 litres,but this doesnt take into account the PPM you are trying to achieve.All iam trying to do is trying to understand more accurately what i am adding to the system and at what levels.I was dosing at 1-3-.5 K-Ca-Mg,but what is that teaspoons,grams what ? and how do you take into account the differences between each nitrient.
I have just been sat trying to work out what i am actually doing,as in a teaspoon of Potassium Sulphate gives me what PPM and then if your dosing Calcium Carbonate and you want a 2-1 ratio how much Ca do you need.
Say a teaspoon of Potassium sulphate is 5 grams,in a 1000 litres this would give a PPM of 2500,if i wanted 200ppm it would be 200/% of k 50% so 200.0,5=400,400/1000 gives me 0.4 mgl. my system of 6000l would need 2.400mlg or 2.4 grams,not 30 grams as i have been adding.
Then if i wanted a 2-1 ratio with Ca how do i work this out,i might be totally wrong and thinking about this in the wrong way but i am just trying to understand more rather than just chucking stuff in and hoping for the best.

Why the Potassium Sulphate and not Potassium bicarbonate?... Is this simply for nutrient deficiency issues and not pH?

I would be very hesitant to use two Sulphate based products. I ran into issues with Sulphate toxicity a while back when using Calcium hydroxide and Potassium bicarbonate to raise/buffer pH, and Magnesium Sulphate just to balance out the 3-way Ca-K-Mg relationship.

The Sulphate toxicity issue came about after using Calcium hydroxide, Potassium bicarbonate, and Magnesium Sulphate in a 3:1:1 ratio over a period of a couple of months. I then reduced the amount of Magnesium sulphate I was using by half and this rectified the problem... So if you were to use your Potassium Sulphate and Magnesium Sulphate in the ratios required to maintain the Ca-K-Mg balance, I would envisage you possibly running into problems with excess Sulphate in the system.

I haven't looked at this stuff in years so don't hold me to it

The Molecular Weight is the number of grams/mole. The Molecular Weights you gave;

Potassium sulfate is 174.2592 grams/mole --- K2SO4
Calcium Carbonate is 100.0869 grams/mole --- CaCO3
Magnesium sulfate is 120.366 grams/mole --- MgSO4

I'm just going to assume you have all of these formulas right but if you are using Magnesium sulfate in the form of epsom salts then this molecular weight is not correct because several water molecules will be attached and this will affect the calculations. Check the container and it may say the formula. I think epsom salts are usually MgSO4*7H2O

Basically moles help you work with tiny atoms and molecules and a mole of any given atom or molecule is defined to have 6.02 X 10^23 of that atom or molecule.

So if you dissolve 174.2592 grams of K2SO4 in 1 Liter of water (1 Molar solution = a mole of the chemical dissolved in one liter) you get 78.1966 grams of potassium dissolved in the liter based on their being 2 potassium atoms in the formula and the atomic weight of Potassium from the periodic table of elements being 39.0983.
.
If you did the same to Calcium Carbonate you would get 40.078 grams of calcium in a liter.

For magnesium it would be 24.305 grams (unless you have the formula wrong)

Obviously you don't have to make up a solution using these quantities since you're looking for PPM (mg/L) amounts, this just gives you a common frame of reference and you can figure what you need for the volume of your system. PPM and mg/L are synonymous in this case - here's someone else's explaination of PPM/ mg/L - http://www.milwaukeeinstruments.com/pdf/mg%20per%20liter%20and%20ppm.pdf

Hope this helps (also hope I got it right since it's been a long time since I've done much of this )

For Potassium

(78.1966 / 174.2592) * X = 2 mg --- Solve for X

X = 2 / 0.44874 =
4.44569 mg of K2SO4 would give you 2 mg of potassium and when dissolved in 1000 ml it gives you a 2 mg/L or 2 ppm solution.

-----

for Calcium

(40.078/100.0869) * X mg = 1 mg

X = 2.4975 mg CaCO3 to get 1 mg Calcium and dissolve in 1000 ml for a 1 mg/L or 1 PPM solution.

-----

For Magnesium

(24.305/120.366) * X mg = 0.5mg

X = 2.4761 mg of MgSO4 to get 0.5mg of Magnesium and dissolve in 1000 ml for a 0.5 mg/L or PPM solution.

Feel free to butcher this if I've screwed up. I never enjoyed chemistry very much.

Hells bells, you guys have just dome my head in. What are you talking about?

I thought it was little moles burying into an ap system. That sounded like fun.

Mr Damage this is just trying to work out amounts,PPMs,ratios etc,this is not dosing for my system,i am just trying to more fully understand what i am adding and the amounts into my system.i used your ratio of 3-1-.5 with success,basically i was trying to make my dosing more accurate as opposed to just measuring out in teaspoons.I have a small set of scales,so i would rather measure weigh out the amounts,then with data collection i can work out what ppm/mgl to dose and at what period of growth,this wont most probably make any difference but its worth doing i think.

Basically moles help you work with tiny atoms and molecules and a mole of any given atom or molecule is defined to have 6.02 X 10^23 of that atom or molecule.

So if you dissolve 174.2592 grams of K2SO4 in 1 Liter of water (1 Molar solution = a mole of the chemical dissolved in one liter) you get 78.1966 grams of potassium dissolved in the liter based on their being 2 potassium atoms in the formula and the atomic weight of Potassium from the periodic table of elements being 39.0983.

That got me for a bit,but that is exactly what i was looking for Scotty,the point to all of this is just the fact of me understanding more fully how much i am adding into the system,using the Damage Ratio 3-1-.5 with what ever combination of nutrients i can work out a mlg weight to add rather than just guessing with teaspoons,this most probably wont make a bit of difference as with no test equipment to validate the amounts that have been added its not very relevant,but its just the understanding bit for me...

Don't forget to check the formulas

Awesome Scotty,just worked it all through.......I will have to have a beer on your behalf this evening.....

It's always better if I get to have them myself Andreas

Cheers