Barb swims like its bent

[snowyangel]

I just noticed today 1 of my barbs(the biggest and oldest) swims like it's bent or curved at the mid section. I'm currently trying to reduce my nitrites(at 0.5) and it seems to be going good, but none of my other barbs are doing this. I've never experienced this before. She still eats perfectly fine and has no visible damages to her like scratches or redness of anykind. Actually it seems like she had some very light black showing up on her back. Could it be her exposure to the nitrites(its been a week and half reducing them)? Please help

 

[7chanaa]

dont worry. it has happened to my angel. it has been like that for a week. but no harm done. so dont worry. if in doubt ask a person from a aquatics shop about it.

good luck.