I don't know much about loaches, but to hopefully help you get a faster response, can you post your ammonia, nitrite, nitrate, ph, temp, size of the tank, tank mates, and if anything has been added within the past month?
ammonia 0,nitrite 0,nitrate 20, ph 6.4,34gal long, and theres 10 khulis, 10 mollies and loads of guppies. and no i havent put anything in over the past month
http/www.fishpalace.org/Disease.html#External
check if u could find ur disease here. Or try to find in our forum, see if the fish have other sign of infection beside stomach getting big or maybe due to over feeding ?
Can the fish maintain it's balance in the water, are scales prutruding out, could be constipation try some shelled peas and daphnia, what do you feed the fish, and is the fish still eating.