Is This A Fin Rot?

[zosiakiwi]

Hi,
Yesterday I have noticed that one of my glowlight tetras had a rotten fin, today it got worse. Some of the fin's edges of other tetras are white. My tank is quite new, 3 months. It is 70 liters. I do a water change 10l every week and test water before every change, no problems here. I have 6 tetras and 4 zebra danio and 1 bristlenose Plec. Tank is clean. Should I get some antibiotics.
Thanks for any help.

 

[WILDER]

Any fin nipping going off, white edges is finrot.

Check the fin for red streaks.

Look under finrot.
http/www.fish-disease.net/diseases.htm