If the damage was severe then it is not reversible.
Different water conditioners are not going to do a lot, especially if it turns out to be internal parasites.
If you just cleaned everything out, including filters, then your results should be 0 as the tank will cycle again. Give it 7 - 10 days then re-test. Many additives stuff up test readings so the water conditioner might be doing this. I don't know, I know Ammolock does.
Hidden parasites are internal. Look for skinny fish, reddened gills, loss of appetite, clamped fins.