selective focus of an amazon sword leaf (echinodorus amazonicus) yellowing due to lack of nutrients in the water

amazon sword underwater plant water garden aquarium aquatic waterplants cordifolius plants planted tank aquascape echinodorus nature freshwater vallisneria spiralis algae light natural group nitrogen deficiency fresh maintenance fertilizing fertilization low tech high aquascaping fertilizer hardness nutrient deficiencies nutrition magnesium potassium selective focus leaf amazonicus yellowing nutrients