The idea of EI is non-limiting factors. Starting at a lower number doesn't allow you to see where you're limiting, and numbers can vary drastically between tanks. One tank I dose over 5ppm P weekly. Other tanks, less than 1ppm. Its a lot easier to start at a higher number and reduce (and remove excess with w/cs).
Your plants can only grow as fast as the least abundant resource available (Liebig's law of the minimum.) Since you mentioned green spot algae, it may be that you're already limited on phosphates.
Grow plants, don't fight algae.