Treatment for disease

I have a quite densely planted 4 ft tank with driftwood, and I have just
discovered that 3 of my clown loaches have ich.  I find it virtually
impossible to catch them to transfer to a quarantine tank.  Is there any
way I can treat the fish in the main tank without affecting the look of the
tank, ie. water turning green color due to the medication, etc?  What can I
use for treating ich without affecting my plants?