Still useful for those of us with floating or emersed plants, not to mention it never hurts to understand why plants need particular minerals.
I find that although I'm not good enough to diagnose exactly what's missing, I can get good results by increasing potassium and/or trace elements.
My thoughts exactly. I know it's terrestrial plants. However, I find it extremely helpful knowing what a magnesium for example is a component of chlorophyll. No Mg no photosynthesis and how iron is required for photosynthesis,