Sword plant macro fertilization
I have a few sword plants that show signs of macro elements deficiency. I started adding liquid N, P and K to water column but while other plants responded to that, swords did not. Is the only way to fertilize swords with root tabs? I did use Flourish tabs a month ago but they made no difference. Amounts of N, P and K seem to be minuscule in them. API tabs have more but not terribly much either and they have bad reviews.
Now I heard about osmocote but am weary. It's really not made for aquariums. Will it endanger my shrimp? Is there a risk of too much N or P leaking into the water column? What exactly is safe dosage?
What would you recommend?