All plants need nitrogen, phosphorous, potassium, carbon, calcium, magnesium, trace elements, etc. in order to grow well. Terrestrial garden plants need these elements and you fertilize to provide them. Aquatic plants need them too, so most of us fertilize KNO3 for nitrogen and potassium, KH2PO4 for phosphorous, either CSM+B, Flourish or TMG for traces, and carbon dioxide or Excel for carbon. That's what you need to do.