Rex - here's the math for the 13% iron chelate:
We want to raise the amount of iron 1ppm in 1 gallon of water. 1ppm = 1mg/L. 1 gallon = 3.785L. We need 3.785 mg of iron to achieve 1ppm (3.785mg/3.785L). In are chelate we have 13% as iron. 3.785mg/0.13 = 29.1mg
That means we need 0.0291 g of this 13% iron chelate to raise the Fe concentration 1ppm in 1 gallon of water. This is for dry dosing only and the equation is: grams = g*r*0.0291
g = water volume in gallons (typically multipling tank volume by 0.85 gives us water volume)
r = the raise of iron in ppm
Only if you have a very large tank, dry dosing is practical. Most of us would want to make a solution though and I'm not so sure what solution Rex is using (don't know how much 1 tablespoon is in grams). Rex, do you have an accurate scale? It would be helpful to know the density in say, grams/tablespoon since most of us would use measuring spoons.