Other than take the carbon out (which is #1) ...
you can wait a few hours to add the ferts... it should be ok. I only use liquid ferts in one tank. I always added it the next morning after water changes. All my other tanks use stuff in the substrate. (they are all different)
I have one tank that is using plain sand with tetramin tropical tablets(food) just shoved in the sand by the roots. I read somewhere that it worked. It looks like they were right. I shove in about 1/2 tab for decent size plants and 1/4 for smaller ones. I add them about every other month... or when they look needy or growth slows down. They are doing just as well as the ones that have the actual plant tabs (which cost a lot more...)
If losing the iron is the main concern... You can add something like pure laterite (clay) to the substrate to provide iron.
Can you tell I am into plants
... I didn't think so...