Weighted measurments vs volume measurements

[james120]

Hey guys. I have been using coral essentials magnesium up for sometime which is based on randy holmes. On the back of each packet it says to use 161 grams of Magnesium Sulfate and 262 grams of magnesium Chloride to make a total of 1litre of solution. I recently decided to buy the raw materials from a reefsafe chemicals company because it was considerably cheaper. The problem im having is that the 3 cups of magnesium sulfate weighs 817 grams for 3.8 litres, which works out to 210 grams per litre which is 50 grams more than the other company which is also just raw materials.

Wondering why this is.
Which one to follow?

any help is greatly appreciated
@Randy Holmes-Farley

 

[Biglew11]

Powders can settle alot during shipping or just handling. This makes them denser. So one cup of a product that settled alot would weigh more than one cup of a product that hasn't settled. This is why it's recommended to make measurements by weight rather than volume.