Nematodes- to treat or not?

[AyalaCookiejar]

Yes, I heard they do best in groups of five or more.. My brothers Molly died and his two loaches cleaned it right up 0_0 plus, he has a pleco, and the loaches are always hiding in the gravel. What an exciting tank, lol. It looks like its empty.
Anyways, I'm always concerned that his loaches are dead since they never come out of the gravel. I am currently trying to get him to switch to sand substrate and add some more decor, but he just wants more loaches *facepalm*