Hello everyone,
Thanks for all the responses. My leopoldi is now back to normal. Just want to share what I did. Transferred to a 50gal hospital tank with lots of aeration, put Furazan Gold, half dose only for 1 week. 25% water change daily. Feed him 1 shrimp without shells 1" size, 3x a day. Which means, very little feeding until the bulging anus disappears. After it disappeared, I gradually increase the feeding. He is now feeding normally ang hoping that he is 100% okay.