Trace element mixes are just that. They do not substitute for anything else. If you have or don't have CO2 you need to supply the macro nutrients as well as the micro nutrients. If you use Excel, you will have less usable carbon for the plants, and you still need to supply the macro and micro nutrients, but less of them. If you don't supply any source of carbon, and have low light so the plants can get enough carbon from the natural sources, you may still need to dose macro and micro nutrients, just less of them.