If the tank was only set up two weeks ago it is very likely not cycled. What are your parameters: ammonia, nitrite, and nitrAte measurements?
By looking at the picture the fish look bloated. If that is also food in the net with those babies. Looks like way over feeding. Looks like old flake food in the tank that rots. Fish will pick at old flake causes a load of problems. bad water quality bacteria and fungal infections including gas and bloat.