There are companies that can test your water for a small fee providing you with a list of what is in the water. Usually they list it as mg/l and thats the same as elemental PPM. Elemental PPM is your true PPM, electronic meters simply use conductivity to estimate your PPM however different compounds in the water will conduct at different rates meaning your meter isn't reading the actual elemental PPM.
Magnesium Sulfate (Epsom Salt) or Mg2SO4 is comprised of 2 magnesium atoms, a sulfur atom and 4 oxygen atoms.
If we take the atomic weights of the elements, determine what percentages are Magnesium and Sulfur (oxygen is a large part of the mass), we can then calculate how much Magnesium and Sulfur are being added be mass. Of course Epsom Salt likes to grab up water so these numbers are only truly valid if you dry the epsom salt first lol.
If we are talking dry epsom salt then adding 1 gram to a gallon will provide an elemental PPM of Mg=26 and S=34.
When I was running coco I had to add a gram per gallon in veg and 2 grams per gallon in flower. I was running RO water and already had the 5 mL of calimagic as part of my soil recipe. So the coco fix was adding the epsom. 5 mL of calimagic fixes my RO water (for any growing) and the extra epsom is a coco fix. Of course you want to keep the overall PPM acceptable so you may have to reduce your A&B parts by a touch.
Hope that all makes some sense, I am pretty baked and somewhat distracted.
This thread really explains things better, note there are a few math corrections in the thread after I couldn't edit the first post, give that a good read and you will really understand how your feed mix numbers can be quantified.
Understanding and Calculating Nutrient PPM PPM (Parts Per Million) can seem like a mystery but it’s actually very simple. Basically the idea is to quantify how much “stuff” is in your water. PPM is commonly measured by a grower using an electronic pen which measures the electrical conductivity...
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