I purchased five male fancy guppies a few weeks ago. They all seemed to be going great, until a few days ago when I noticed one seems to have strayed from the pack. The other four swim around the tank together constantly, but the other one is just hanging around the far corner of the tank by himself. The heater I have for the tank is also in that corner along with the filter, and all the fish seems to be doing is nipping at the rubber on the heater (or at least, I presume that's what he's doing--he's too small and oddly positioned in the tank to get a good view). He's eating normally, and he's not really exhibiting any signs of diseases that I know of (I'm new to this, so I may be wrong). Is it normal for some guppies to be anti-social?

What size is your tank and what are your water params?

Usually guppies stick together i have not had some in a while but if you could answer the 2 questions i asked then we may be able to tell you why your little guppie has strayed from the pack.

I've found tropical fish that hang out around the heater are usually sick, does he show any signs of illness?