Yes plants do need CO2, light and water. but they also need Nitrogen, potassium, calcium, magnesium, phosphate, sulfur, chloride, iron, manganese, boron, zinc, copper, molybdenum and nickel. these items are found in fertilizers or steam and lake water with growing plants. typically plant growth issues are not caused by CO2.
if just one of the 14 nutrients is missing plants won't grow or grow very slowly. While your tap water typically has some calcium, magnesium, sulfate and chloride it may not have amy of the metals such as iron. you might not need CO2 it yo have an air stone our if you have some ripples on the surface of the water due to the pumping the filter.
if you don't vet have plants try a floating plant such as Redroot floater or salvina. if these do well you might be able to grow plants with little effort. IF The plants don't grow wo the leaves die or have holes in them you might need to fertilize the water.