Nanaof4

Thanks. Dumb question, what test should I look for for the salinity? When you say slow, over the course of a few days, a week? Which antibiotics work best? Sure hope I can catch the little stinker! Thanks again. Is it contagious and will the fin repair and grow back?

0 ammonia, 0 nitrite, 5 ppm nitrates, 6.8 ph, 78 degrees, all male tank, his tail wasn't as big as the other Blue, but now it's all ragged and looks to have holes? New to the hobby. 3 months in and this is my first issue to speak of. Any thoughts are appreciated.