Two things. One, Amazon Sword are heavy root feeders so starting to dose frets in the water won't help much. Two, O+ tabs can take up to a month to start working but should fix most standard deficiencies. My swords looked horrible but a month after adding the tabs they are now growing like crazy.
However, if you don't have co2 then the tabs won't help much since co2 deficiency causes the same problems as many macro and micro deficiencies, no matter how much ferts you add.