about a year maybe two i had 3 whites of a friend that couldn't look after them anymore. they were only young so i had to keep them in a separate tank from my original one. as they grow i put them all together. the thing now is 2 have grown loads and there is still one thats the same size as when i got it (thought it maybe a male). not been a problem before but today he has gone down hill loads. can't get him to eat so i've taken him out and put him in a small tank with paper towels and heat mat. any idea what could be wrong with him? why wouldnt he have grown?