EI was always a little difficult to do even with water changes. Not sure what size system you have, but the problem gets worse with a smaller tank.
If you really want a dosing system that works, I'd highly recommend using dry ferts from Green Leaf Aquariums. Invest in some lotion bottles that dispense 2ml per squirt, and use Zorfox plant calculator to make your fertilizer mixes. Still requires about a 50% WC every week, but produces great results. Planted tanks used to make me tear my hair out, but now this system has made it enjoyable.