What is the target Fe?
Well that is your call in some ways, as to what fe ppm to aim for can be a controversial subject IMO, Here are three popular dosing regimes

All work for some folk yet the weekly [Fe] varies nearly ten fold. so if you have added all 50g in 500ml I would add say 1ml a week to start with and see how it goes and watch your plants, I would dose it at night/lights off with it being photo sensitive, although @ceg4048 did say that after a couple of hours plants have had their fill