Hi Chukuna, from the problems I've had recently, I think you may suffer the same. If you have too many fish and the tank isnt cycled properly and completely, then your fish start to die. Its really awful. Read some of the other posts here and ask questions about "cycling" if you don't quite understand, I didn't! You may end up with an ammonia problem when all those fish start peeing in your tank and the good bugs aren't quite ready to clear it out of the water. What sort of filter have you got? The experts here will be able to advise you what to do, so don't be afraid to ask LOTS of questions, they are really friendly. Good Luck