After reading this post I can confirm I also have the same plant in my tank and had no idea this needed fertiliser. I’ve heard the salt minerals I use are good for plant growth though.
Yes, but that is just dealing with the "hard" minerals, primarily calcium and magnesium. But plant nutrients come from fish foods too.
Different plant species have differing levels of nutrient requirements. It is certainly possible to have live plants growing well in a tank with fish and no additives; my 10g is like this. But the plants are low-requirement. Higher requirement plants will do better with some supplementation, but one doesn't want to overdo this as algae can then become a nuisance. It is all about balance.
I have kept Amazon sword plants for decades, as I find them one of the easiest plants under the moderate lighting I provide. I have grown them with no additives, with liquid additive, with tabs, and with tabs and liquid. They survived in all situations, but really thrived in others.
My
Echinodorus major which is now in my 70g is presently in flower, for the third time since I have had this plant (nine years). This is the only species of
Echinodorus that will produce flowers along the inflorescence when the parent plant is grown permanently submersed. All other
Echinodorus species require emersed growing in order to produce flowers; they will produce adventitious plants along the inflorescences when grown permanently submersed, and if conditions are to their liking. Some of my common swords,
Echinodorus griesbachii [this is now the accepted name for
Echinodorus bleherae], have in the past produced three and even four inflorescences at the same time, and twice every year.
Here's a photo of the
E. major flowering back in 2017, and today. This is the second flower inflorescence in as many months from this plant, and this time I am letting it grow out of the tank as I have previously kept it under the cover glass as in the older photo.