Hey Paulo,

There's only one real way to determine ppm and that is to use the molar weights as percentages of the weights you are using. Just google for the molar weight of the compound. Start with KNO3 for example. You'll find the following;

**Element____# of Atoms____% by Weight**
Nitrogen________1______________14%

Oxygen_________3______________47%

Potassium_______1______________39%

So Nitrate is NO3 right? this means 14% + 47% = 61% of the total weight of KNO3 is made up of nitrate.

So, if I add 1 gram of KNO3 to 1000 L of water that would give me 1ppm of KNO3, comprised of 0.6ppm of NO3 and 0.4ppm of K.

The concentrations are easier to manipulate if you work in multiples of 10. PPM is really 1/1,000,000th which is the same as milligrams of something dissolved into kilograms of something else. So 1 gram KNO3 to only 100 L of water gives me 10X the concentration (i.e. 10ppm KNO3) or 6ppm NO3 + 4ppm K.

If the numbers are not multiples of 10 then you have to use the brute force method and simply figure out how many miligrams you're adding to how many litres. Then divide the two, viola, instant ppm. The problem only becomes sticky for those wimpy people who dose pre-mixed solutions. They have to figure out what the ppms of their mixture is and then how much dilution is occurring based on adding the solution to the tank. But again, as long as you understand the concept, then this is only a minor annoyance. All dosing calculators, such as nutricalc as well as

JamesC's Dosing Calculator have to use this same principle.

So lets say you made a macro solution using 33 grams KNO3 in 250ml water.

We know that 33 grams is really 33,000 mg and that 250ml water is 0.25L (0.25Kg).

Therefore that mixture is 33,000mg/0.25kg which is 132,000ppm KNO3. We also know that of that 132,000ppm, 61% of it is NO3, so this macro mixture has more or less 82,500ppm NO3.

OK, so lets say I went postal and dumped all of this 250ml solution into a 100L tank (I'll just assume there's 100L of water in it). Can you see that it would be the same as dumping all 33 grams of powder into the tank? So the concentration of the tank would be 33,000mg/100Kg, or 330ppm KNO3 (201ppm NO3).

So for a 100L tank, since adding all 250ml of this solution would add 201ppm NO3 then each 1ml of the solution would 1/250th of this, i.e. 201ppm/250ml = 0.8 ppm per ml. EI standard dosing is on the order of 20-30 ppm NO3 per week. For a 3 dose per week schedule you could add 10 ml per dose which would be 10ml x 0.8ppm/ml = 8ppm per dose. Dosed 3X per week would give you 24ppm per week. If you dosed daily, I'd pick a number like 28ppm per week, which means 28ppm/7days = 4ppm per day. To get 4ppm per day you'll need to dose 5 ml per day (nice round numbers).

If your head is spinning by now then it's just as easy to use either nutricalc or James' calculator because it does the same gymnastics within 0.33 milliseconds.

Cheers,