Are you using regular aquarium gravel? Or something like eco-complete type gravel that holds in nutrients to later release back to plants?
Are you using root tabs for the plants?
It sounds to me like the plants aren't getting the nutrients they need, and there's simple ways to correct the issues. 1) Adding root tabs to the substrate under the plants. 2) Going with a better planted substrate thats made for planted aquariums.
Eco-complete and Flourite are inert planted substrates that are capable of storing nutrients from the water column, and slowly releasing them back to the plants over a period of time.
As for liquid carbon supplement, most of them are active for 24 hours and then needs to be added to the water again. Your best bet would be a co2 injection system since your work causes you to be away for periods at a time.
As for the lighting I suggest getting some sort of reflectors for it.
As for EI dosing, you can go with a regime to fit your needs as well as the plants needs, I'm sure someone here knows more about that I do lol