black fins

Hello fish community! I have 4 honey gouramis that I have had for almost a year now and two are turning black. They sort of looked like they rolled around in mud, it’s covering their fins and body. One looks more black then the other but I want to make sure this doesn’t spread to any other...

Hello. I've woken up today to find that some of my neons, particularly the dominant male, are acting rather aggressive. Many of them, including the dominant male have developed a black tinge to their fins. This happened around a month ago, then it went away. I've tried looking for the cause...