Doesn't sound normal for a Colombian shark. If you have this fish in a freshwater tank that has not been cycled and is too small, then you have yourself a problem.
Colombian sharks ARE NOT freshwater fish. In fact, they need Brackish water (salinity of 1.005) when young and as they get older, full on Saltwater conditions of 1.020-1.025. It will die in left in freshwater. You should slowly acclimate the fish to Marine conditions over a matter of months. To know what salinity your water is, you will need either a Saltwater hydrometer or better yet, a Refractometer. Use Marine salt only and never table salt or Aquarium salt.
Also, CS' can grow up to 20 inches long and need at least a 100 gallon tank to sustain one. There is no use keeping a fish in a 10 gallon tank that will die if left in there just because it needs more room.
If you can't afford or maintain this fish's needs, then I suggest you return the fish (which would probably not help) or a better alternative is to find someone who knows fish and has the room for a Colombian shark. Otherwise, you have some investments to make.
