Most loaches are considered scaleless, dojo's included.
Best approach is to quarantine new fish to prevent an infection in the main tank, and monitor water quality closely. Feed an appropriate variety, follow a regular maintenance schedule, ect. Prevention is always best.
If your main tank becomes infected, you'll need to make a decision. If possible, remove the ailing fish and treat in a separate tank, appropriately for the species. If you can't do this, then you will have to treat at a half dose (most instructions will include this info). This means you'll be treating longer periods of time, so you'll want to monitor the tank and fish closely. Some medications will hinder your bio-filter, and longer treatment periods increase the odds of a mini-cycle.