Ok, so I've totally murdered my cycle and I'm in the process of fixing that but I've noticed that 2 of my boys in my destroyed 30g have black on the edges of their fins. Also, I have another fish who is completely seperate that is also showing some blackening. This seperate fish and one of the boys in the 30g are both new fish that I bought at the same time and store. Is it possible that they have fin rot and it's spreading in my 30g?
If they do have fin rot, what's the best way to treat it and should I remove all the fish from the 30g and scrub it and start the cycle all over?
Also, I have a female that I bought with the infected(?) males, should I also treat her and my other female(they are in the same tank) to be certain that they do not have fin rot as well?