Signs such as slow growth, thin, spindly leaves and stems, yellowing leaves, pale veins, etc., will indicate that a supplement is required.
Every aquarium is unique, so it is advisable to watch your plants over the course of the first month or two and look for signs of deficiency. Generally, this will be in the form of nitrogen, iron, potassium, or trace element deficiency. Signs such as slow growth, thin, spindly leaves and stems, yellowing leaves, pale veins, etc., will indicate that a supplement is required.