Steer away from the Rid-Ich since I believe this is a malachite green and formalin combination that'll have little effect with argulus (fish lice). Your better bet would be Fluke Tabs since there's no malachite green or copper that may burn your loaches and irritate the wounds at the anchoring points of the parasites.
After the lice are gone, treat with a broad spectrum antibiotic, for secondary infections and keep the temp elevated to deflect a possible fungal infection. Once the fish's slime layer is restored, you can return to normal maintenance regimens again. Good luck.