I've got two small-ish Kuhli loaches in a 20 gal tank along with a sprinkling of other fish and they have been doing fine for as long as I've had them (~2.5 weeks). However, a few days ago I noticed that one of them seems to have lost some coloration on one side of his body. Any ideas as to what might cause such a thing? Is it genetic? An injury? I'll post a pic as soon as I figure out how to do it here....