we had a massive outbreak of ich recently.. we used ws3 to eradicate it, but it did take 3 weeks. we lost one baby loach and one platty because of it. we were advised to maintain a pH of 7.2, to raise the temp to above 80, as this speeds up the life cycle of the ich, and to follow the directions on the bottle of medicine.
once the ich has appeared on the fish as white spots, it is already present in the water. the ich can lay dormant in the fish and then appear for another reason such as stress.
i would continue to treat the water, you could remove the tetras if they look fine, but if you treated the water soon enough, then hopefully all the ich in the water has been killed, and the tetras won't show signs of having ich. you just need to wait for it to move off the loaches (i was told that you can't kill the ich, when it is on the fish, have to wait for it to move).
i hope that helps.. there is a lot of much better advise on this forum if you look around. but hopefully you caught the disease soon enough, and you wo'nt have a massive problem!
good luck
