First off, Neptune's Harvest is a brand. Which of their products are you referring to? I don't know of any NH ferts with an NPK of 7-4-3.
What matters most about the fertilizer nutrient levels is the ratio of each nutrient to each other one. For example, a fertilizer with an NPK of 1-2-3 would work the same as a 2-4-6 fertilizer made of the same ingredients, you just have to use twice as much. The NPK #'s are the percentages of each nutrient in the fertilizer before mixing and they always become far more dilute after mixing. That 1-2-3 fertilizer might end up closer to .01-.02-.03 in the final solution. So, the base fertilizer might be weaker than another, but that only means that you'll mix more of it with water. So again, the important part is how much of one nutrient there is in relation to the others, because you can't separate them.