I am sorry to hear your bad luck of introducing ick from new clown loaches. I share your grieve as I lost all three of my decade old 8+ inch clown loaches last week to ick. It all started after I introduced a dozen CA juvies from my grow out tank, which I treated with ick a month ago. I examined the juvies carefully that there were no symptoms of ick before I introduced them to the clown loach tank. I was wrong. Two weeks later, symptoms of ick showed up by behavior and a few white dots in one fish. I immediately administered Super Ick Cure (malachite green and formalin combo) which I have successfully treated ick on CL many times before. But this time I was out of luck because had to go out of town two days after treatment. When I returned home 4 days later, the CL were peppered with white dots, heavily breathing, and all 3 died in three days. All other fish are healthy with symptoms.
The lesson I learned is that fish can carry low level of ick infection with no external symptoms for weeks. Some claim that ick spores are always present in the tank and waiting for stress to break out. I have never experienced ick outbreak spontaneously without introducing new fish, so I am doubtful the claim is proven.
CL is magnet to ick and is fatal if not treated early and continue long enough, at least a week, to root out the disease. I have no problem using MG treatment on my scaleless bristle nose at full dosage. CL is actually not scaleless but has very small scales. But the label says that MG should not be used for Elephant nose or Rays so you have to look for alternative treatment, such as salt or copper. I would remove the CL and treat them separately from your Rays.