hello to who ever reads this post

i have a question for you.
i have a 20 gallon tank which has plants in it along with fish.
im planning on getting more plants after christmas hopefully
now i know for keeping plants you ideally need a rich substrate so im using "eco complete"
and the liquid ferts im choosing to use are "seachem"
seachem trace, seamchem flourite and seachem nourish...here's my question how do you use liqiud ferts? do u poor the ferts into the cap and then directly into the tank?
or do u mix it with new water on a water change?
or does it matter either way?