It was the LFS owner who told when we were talking about why so many of my plants were either so-so,of dying off. IRON!..You got to use iron. He was right.
There are many other elements required besides Fe. One of them is also zinc in trace amounts.
Get it as green as can be and IF the test kit says I have say,5x what they recommend? I will keep it at 5x since the fish are fine and the plants growing.
With too much there can be a toxic side to this or another element shows up lacking.
Good luck and don't remain @ the alchemy stage for too long.!