It's almost certain you did not introduce the ich with the algae. Fish parasites exist in almost all marine aquariums; the fact that we have closed systems just make the fish much more susceptible to getting nailed by them. I'd add a cleaner shrimp or two to your 10 gallon immediately and see if they can help the clownfish. Sometimes clowns won't go visit the shrimp, and the shrimp may be intimidated by the clowns' natural territoriality. But it's definitely worth a try.