Well first off we need to know what kind of lights you have. LEDs can be very strong or weak.
You may not need to change the substrate it just depends on what kind of plants you want to grow, which depends on your lighting. You see, all aspects of a planted tank revolve around lighting. It dictates what equipment you need, what plants you can keep, what fertilizer to use, etc. Most likely you will be getting low light. In that case I recommend plants like Java Fern, Java Moss, Anubias species, Hornwort, and Anacharis.
If indeed you are getting low light then you should get some Seachem Excel. You see, plants need 4 big things: water (thats the easy one), light, nutrients (aka fertilizer), and a carbon source. Injecting co2 into the tank is used in medium and high light tanks. Remember I said that light dictates everything in a planted tank? Thats an example right there. In low light tanks, Seachem Excel (a product that provides a liquid source of carbon to plants) is sufficient, although it provides less carbon then injected co2 does.
Lastly, fertilizer. Again, the important aspects of planted tanks revolve around light. In medium or high light tanks people usually mix their own fertilizer using dry chemicals and distiller water (hehe, Breaking Bad
), but in low light tanks the waste produced by fish (this is broken down by bacteria that naturally occur in your tank, and forms macronutrients like nitrate and phosphate) coupled with a product that supplies micronutrients called Seachem Flourish Comprehensive, should be sufficient.
