I just started stocking my 55 gallon aquarium about 2 weeks ago. I currently have 2 dojo loaches, 6 congo tetras, 1 rainbow shark, and 1 rubber lip pleco, all of which are very small. I've been monitoring my water conditions and the ammonia and nitrites have both remained at 0 with no fluctuations. One of my dojo loaches looks healthy and is swimming around and eating like nothing is wrong. The other one, however, has seemed to get more and more lethargic over the past couple days. This morning he didn't even come out to eat. I've looked him over and I don't really see anything that I can tell is wrong with him. He looks like me might have some very tiny white spots on his feelers and his fins but they are so small that I'm even second guessing myself about whether they are even there. I just finished my weekly 20 percent water change this morning and when I was finished I reached in and scooped him up in my hand. He just laid there so still for so long that I had decided he must be dead when he swam out of my hand to the bottom and is now just lying there against the front of the tank. All of my other fish are acting and looking normal, even the other dojo loach which I have been keeping a very close eye on since I noticed this one having problems. Does anyone have any idea what could be wrong with the little fellow? This is really bothering me having a problem like this with no obvious causes so soon after setting up my tank. Any help anyone could give me about this would be greatly appreciated.