How do you add more fertilizers?

I normally use a mixture of liquid fertilizers, and will also push down root tabs.

When I used a substrate such as Flourite I mostly just overdosed with liquid fertilizers for it to absorb it (while also placing a TON of root tabs underneath it). Then once I noticed my plants start to look a little poor, I would use more liquid fertilizers and then take some root tabs and try to put them underneath the substrate while filled up with water.