No need to panic, ich is easy to treat. Keep the loaches in, it sounds like they're all infected. Do a 50% water change. Raise the temperature to about 85 and add approximately 2 tablespoons of salt for every 5 gallons. Don't add the salt directly to the tank, dissolve it in some tank water first then pour the solution into your tank bit by bit over 24 hours. Follow this by performing 25% water changes daily for a few days to both remove the salt and to help remove the parasite. Good luck.