Ok so my friends dad has had fish like his whole life and I went to him for tips and stuff. So he has 2 tanks currently, one is 125 gallons and the other is 75 gallons. The 75 is in his office(He's a doctor). So I look in it and it's full of all these amazing cichlids like 14 of them(4-7"), a foot long pelco, and a footlong catfish(I've never seen one like it), then I look in the middle of the tank and notice there is a fish I missed. It's a freaken Black skirt tetra. How has it not died?! He's had him in there for like 5 years and he's in better health than mine and I've got a tank with basically them as the only fish(55 gallon, had it for like a year). I asked him and he was like "I've had like 3 of them to start up the tank when I got it and I've had him sense. Didn't really expect him to get anywhere but he's out lived alot of my cichlids." I was wondering does this normally happen like this? I was just shocked to know this works.