i have a 4 girl sorority in my 10 gallon(im working on getting a 5th but no money.) theres one fish ive had in there all the time, a little pink/purple shimmery girl who always seems to be perky and keeps out of trouble. and every time she gets a nip or 2 shes always fine and is never bothered. well lately she has become very lethargic and lost a lot of color on her body and has no visible injuries. shes still eating(not a lot, but at least 1 pellet twice a day) but she stay away from the other girls and rests a lot. i really need to vacuum the gravel and take all the fish out but im afraid taking her out will stress her out or when i put everybody back in she'll get hurt. i have a separate 1/2 gal tank i can put her in so she can get better but i dont have a heater for it.
ive asked tons of similar questions to this but ive never succeeded in keeping the fish in question alive.