I recently noticed that most of my clown loaches are missing the very end tips to their tails. Dose it look like someone is nipping at them or is is something more serious? I have 12 clowns, 6 around 6cm and 6 between 15-18cm. Tank mates are 2 baby Texas and baby red Severum, bristlenose, L333 pleco and ghost knife. Water is perfect. Ammonia and nitrites are 0 nitrate is about 10. Only the clowns are affected. What are your thoughts?