# How do I calculate fertiliser dosage based on weight percentage?

#### xZaiox

##### Member
Hi guys,

So I recently purchased some manganese to correct a possible deficiency, and I'm a bit confused on how much I need to add to achieve a certain ppm. I normally use rotala butterfly's calculator, and so far I've not had any issues using it for literally any other fertiliser, but this specific one doesn't appear to have a relevant drop-down on the calculator. The calculator has options for manganese chloride and manganese sulfate, but no option for EDTA chelated manganese (which is what I'm using).

The manganese I have is 13% EDTA chelated (Link). If I want to dose 0.1ppm, how much do I have to add to a 180 litre tank? And if somebody could also explain how the calculation is made, I would greatly appreciate it The IFC is your friend for this one . . .

• Hufsa, xZaiox and dw1305
If my maths, and using the IFC is correct, to dose 0.1ppm per week to a 180 litre tank, you'd be dosing 0.138 grams.

Better to make up a solution using serial dilution and dose a proportion of that. For example, according to the IFC if you make up a stock solution you could add, say, 23.08 grams to 500ml of water. Then use 50ml of that stock solution added to 450ml of water to make a 500ml dosing solution. Dosing 10ml of that three times a week should give you your target 0.1ppm.

Hi all,
The manganese I have is 13% EDTA chelated (Link). If I want to dose 0.1ppm, how much do I have to add to a 180 litre tank? And if somebody could also explain how the calculation is made, I would greatly appreciate it
Simple enough when you have the % of manganese (Mn) in the chelate.
• One gram of manganese EDTA contains 0.13g of Mn,
• we need to convert that to milligrams (mg), and there are a thousand milligrams in a gram.
• 0.13g = 130 mg and "mg / L" is the same unit as "ppm" and
• the tank size is 180 L.
• 130 / 180 = 0.722 ppm.
• This is the total addition of Mn in milligrams divided by the total volume of water in litres if we added 1 gram of MnEDTA, we don't want 0.722 ppm, but
• If we divided 0.1 by 0.722 we get ............... the IFC's and @Wookii 's 0.1385 g.
Better to make up a solution using serial dilution
Agreed.

cheers Darrel

• • Hufsa and xZaiox
Much thanks to both of you @Wookii and @dw1305 , and thank you for explaining the calculations Darrel, I'll now know how to calculate any others moving forward. • Wookii and Hufsa
Hi all,
and thank you for explaining the calculations Darrel, I'll now know how to calculate any others moving forward
I just have a <"spreadsheet with a periodic table embedded">, this gives me the Relative Atomic Mass (RAM) of each element.

Then all I need to know is the formula for any compound, to get the Relative Molecular Mass (RMM), and the percentage of the element I'm interested in.

At that point all we need is the tank volume and from there it is a simple calculation.

<"All the nutrient calculators"> are based on the periodic table of elements.

cheers Darrel

• xZaiox and X3NiTH