Quote:
Originally Posted by frostby
How do you read the NPK thing for example one bag says 0050. Does that mean 50% Potassium by weight?
If you mix the above with X ml of H20, how do you know what ppm you will reach when it is added to X gallon aquarium...
I do have chucks calculator, and will use it, but I guess I would love to know more w/o relying on additional tools.

I agree that Chuck's Calc is sweet (
real sweet), but it's great you want to figure this out for yourself.
You're correct about the NPK thing, as 7Enigma said. Pure KCl is really ~52%
K by mass, but such specifics aren't so important unless you want them to be.
To calculate dosing solutions manually, it's easiest to use two steps. First calculate the solution to get grams of nutrient per mL, then the resulting
ppm of the mL dose into the tank.
1)
mg fertilizer = milligrams of dry compound from Greg Watson.
%nutrient = % using that NPK rating
mL solution = how much water you're using for the mix
mg fertilizer * %nutrient / (ml solution * 100) =
mg nutrient/mL solution
2)
Then calculate your resulting
ppm (
mg/L) from whatever dose.
(
mg nutrient/mL solution) * mL dose / (tank gallons * 3.785L/
gal) =
ppm nutrient
For example:
Let's say you want to mix 150 grams of KCl into a 250mL bottle, and you want to know how much 1mL would add to a 20gal tank.
150,000mg KCL * 50%
K / (250mL * 100) = 300mg
K/mL solution
300mg
K/mL solution * 1mL dose / (20gal * 3.785L/
gal) = 3.96ppm
K
Make sense?
Lets say instead you want to use the above mix, but find out how many mL you need to get 20ppm
K into 20gals.
target
ppm nutrient * tank gallons * 3.785L/
gal / (
mg nutrient/mL solution) = dose needed for target
ppm
20ppm
K * 20gal * 3.785L/
gal / 300mg
K/mL solution = 5.05mL to reach 20ppm
K
(As you can probably tell, its way easier to just dose KCl dry. If you want the formulas for this let us know. If this isn't clear or someone could explain better, please let us know.)
Run these calcs by Chuck's and you'll see some difference. Replace the NPK rating with true mass percentage, and you'll have Chuck's Calc's output. (In this case, replacing 50% with 52% for
K from KCl.) Chuck uses best practice by calculating true mass percentage using atomic weights. You could do this with a periodic table, but
here's a handy calc.
If you want to use teaspoons and such instead of grams, you'd have to start with some conversions of course.
Steve Pituch's calculations page is a great resource for this and calculations in general.
Quote:
Originally Posted by 7Enigma
Had you waited to order I would have suggested getting potassium sulfate instead of KCl since adding salt to the tank is not always wanted

Only for your info, Tom Barr's recent newsletter and study finds salt and effects from chloride aren't so important nor dangerous for our purposes.
I've only used KCl and, while people I greatly respect suggest K2SO4 for exactly the reasons you describe, find it fine. I still have 20 or 30 pounds of KCl after spreading it amongst my club and stuff, and plan on sticking with it until I run out. Other people seem to like it too.
Hope this helps.
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