1 of my neon barbs turned skinny and isn't eating it tries to but just spits it back out, the rest are nice and plumped. Inhabitants are 4 female neon rosies( I keep the females separated from Males), 1 bristlenose and 2 cherry barbs. Ph 8.4 ,ammonia 0 , nitrites 0 and nitrate 10. I notice it yesterday but could have started before. I don't see any poop from it so don't know if its white and stringy, anything I can do?