All of us make mistakes, you shouldn't feel bad, your doing whats best by your loaches now
Yes it will be best to remove all the rocks, Im not sure what they leach, perhaps Chefkeith could share a bit more when he sees this.
When adding rocks and decor that you are unsure about into your aquarium (you should really do this with any rocks that you want to add), you can either soak the rock etc in a bucket of water and test the water continuously-for a few weeks maybe and note any changes in pH, KH etc
Another way to test if the rocks are inert is to pour a small amount of vinegar-or another acidic substance. If there is a reaction-fizzing etc, the rock is alkaline.
If you are having problems tracking medication down, could you post your location, there are members from everywere on here so if your having problems theres a good chance someone can recomend were to go.
Ashleigh