My big weather loach is acting listless and hanging at the top to breathe. My other dojo, and the other fish in the tank are doing fine though. The sick loach is also having trouble swimming, yesterday his tail wanted to float and he seems bloated and he/she is gasping. Around the vent is also swollen. I put in some Melafix yesterday and this morning and he/she seems to be swimming a little better, but I can tell it is still under the weather. What could be wrong with this fish? Is it cureable or should I remove him/her before the rest of my fish get sick? What other meds should I use? 
I've had this loach for about a year and he/she has always been in good health till now.
I've had this loach for about a year and he/she has always been in good health till now.