don't feed your fish hamburger. if your fish haven't been in our tank very long, they may just be getting acclimated. feeders can spread disease to your fish. just skip feeding for a day or two then try feeding them some bloodworms. watch them for the feces problems already described. another thing to watch for, if they are in the same tank, is aggression. i bought two siblings and put them in the same tank. they were small, about 2 inches. i had a male and a female. the female was growing like crazy and the male was hiding alot and not coming out to eat. she was kicking his butt when ever he came out. she grew about an inch while they were together. he didn't grow at all. as soon as i removed her, he put on an inch in about two weeks. it has been two months since i separated them now and he is about 5 inches long.