Help on treating ich

[shootingstar]

To answer the question you originally asked.

YES, a DT left fallow (without any fish) for 8 weeks will be generally considered ich free.

Ich is a fish parasite, having fish present is essential for ich to survive and reproduce. If there are no fish in the tank the Ich will die off.

Treat the fish (with whatever method you decide) in another tank and return them to the DT after the 8 week fallow period.
or
Don't treat and use food environmental factors to make them strong enough to fight off the infection that will remain.