Bullying or fin rot? HELP PLEASE!!!!!

[Fishperson]

I have a 20 gallon high that I fishless cycled with ammonia that finished cycling march 8. I added 5 bloodfin tetras on march 8, and then 2 more a week later. I bought 3 rummynose tetras on march 28. I went on vacation the next day, and got back today. I have a tetra whisper 30 filter, have not changed the filter pad yet, and have not vacuumed the gravel yet. I do 5 gallon water changes every weekend. the last time I checked (about 5 days ago) I had:
10-20 nitrate
0 nitrite
0 ammonia
7.4 ph
Right after that reading I did a 5 gallon water change. My problem is that one of my rummynose had his tail fin completely gone when I got home today (the 31st). I think it is fin rot, although it could be bullying. The rummy nose are all smaller than the bloodfins, and 2 big bloodfins chase the rummynose around sometimes, but it doesn't seem to serious. The rummy nose that is affected is the smallest fish in the tank. So, my total stock is 7 bloodfins and 3 rummynose. I took the affected rummynose and put him in a small tupaware container with tankwater, and took some pics of him. I don't want to put him back in the tank unless it is only bullying. I have the other two rummy nose in a cage thing that hangs on the side of the tank, so they cannot interact with the bloodfins, just in case it is bullying (although they are only separated by fine mesh, so the water still passes through). What should I do? If it is fin rot, I think I will take him back to the store, and get some more rummynose. If it is bullying, which is a bit of a problem anyway, I think I will still take the affected one back to the store, and get some more rummy nose. My questions are:
how do I treat fin rot?
is this fin rot?
how should I fix the bullying thing, or is it just a temporary stress issue?
any thing else I should do? Maybe a water change?
here are some pics:

 

[Coyne]

I have a 20 gallon high that I fishless cycled with ammonia that finished cycling march 8. I added 5 bloodfin tetras on march 8, and then 2 more a week later. I bought 3 rummynose tetras on march 28. I went on vacation the next day, and got back today. I have a tetra whisper 30 filter, have not changed the filter pad yet, and have not vacuumed the gravel yet. I do 5 gallon water changes every weekend. the last time I checked (about 5 days ago) I had:
10-20 nitrate
0 nitrite
0 ammonia
7.4 ph
Right after that reading I did a 5 gallon water change. My problem is that one of my rummynose had his tail fin completely gone when I got home today (the 31st). I think it is fin rot, although it could be bullying. The rummy nose are all smaller than the bloodfins, and 2 big bloodfins chase the rummynose around sometimes, but it doesn't seem to serious. The rummy nose that is affected is the smallest fish in the tank. So, my total stock is 7 bloodfins and 3 rummynose. I took the affected rummynose and put him in a small tupaware container with tankwater, and took some pics of him. I don't want to put him back in the tank unless it is only bullying. I have the other two rummy nose in a cage thing that hangs on the side of the tank, so they cannot interact with the bloodfins, just in case it is bullying (although they are only separated by fine mesh, so the water still passes through). What should I do? If it is fin rot, I think I will take him back to the store, and get some more rummynose. If it is bullying, which is a bit of a problem anyway, I think I will still take the affected one back to the store, and get some more rummy nose. My questions are:
how do I treat fin rot?
is this fin rot?
how should I fix the bullying thing, or is it just a temporary stress issue?
any thing else I should do? Maybe a water change?
here are some pics:

Im pretty new to this, so keep that in mind. However, Ive been reading A LOT the past couple weeks.
First, I would post in the "Unhealthy Fish" area if you have not already.
I havent done any research into health problems yet, so Im useless in identifying fin rot.
Also, you posted your water readings from 5 days prior to the fin problem, did you happen to take one the day it happened? If so, how did they look?

If it is stress related bullying then there are some things you can look into: Are they staying fed? You mentioned this happened after you had been away for a few days. If they get hungry then they can get cranky and take out their frustration on the easiest prey the can find (ie the smallest fish in your tank).

How is your tank set up as far as cover goes? Places to hide or break up the line of sight of the two schools? Fish have short memories, so if a bullied fish is able to hide for a bit, the offender will usually move on to something else.

Adding more Rummynose may help. One of the reason fish like to school up is because other fish start seeing them as one larger entity instead of a bunch of small, individuals. The folks at my big box LFS suggest 3 min for schooling fish, but the folks at the more specialized LFS say 5 or more depending on the fish (and tank size). For example, I currently have 7 Serpae Tetras and will soon be adding 9-10 Harlequin Rasboras since they are a little smaller in size.

Like I said.. Im new at this, so all my advice (if you'll allow me to call it that) is purely academic and not based on real life experience. Just stuff Ive picked up from reading and conversations with people who have been doing this a while.

 

[spiketooth]

Little hard to tell, looks like fin rot becuase the white tips of whats lat the end of his tail

 

[Fishperson]

My tank does not have enough cover, I know, but bloodfins are supposed to be nice. I only added just 3 because I was afraid that if I added 7 at once it would start a mini cycle. The one that was really bad died overnight. He had trouble swimming. I had him in a separate container anyway. I put the other two rummynose back in the tank today. They are getting harassed a lot by the whole bloodfin school, but there is no nipping. I don't know if these have fin rot, so I am going to wait until tomorrow to see if it progresses. I think I will do a gravel vacuum/water change later and check the parameters afterward. Should I put the rummynose back in there separate enclosure (it is a cube that hangs on to the inside of the tank with mesh separating the fish in it from the ones out of it. It is very useful, I think it is meant for fry but it has dozens of other uses) until tomorrow, when I can check on them again and maybe take them back?

 

[Fishperson]

THANK YOU SO MUCH COYNE!!!!!!!!!!!!!

I just gave the fish a bit of food, and they all went crazy!
Before I left, I figured that since some people do "fast days" then mine would be okay if I just fed them a lot before I left. Well, I guess they were so hungry that they were venting their anger on the rummy nose. I knew something was up because the fish with an already torn fin didn't get fin rot. I think the one with barely any fin had it, and that all of the rummy nose were just bullied a bit. I will wait to tomorrow to bring the dead one in and get more rummy nose then.

 

[Coyne]

Glad to hear there was an explanation/solution, but sorry to hear the little guy didnt make it.
Ive heard of people fasting their fish as well, but I think its typically just for one day every week or two. Im going to give this a try with mine and see how it goes. If anything I tend to overfeed, so one day a week of no food might be ok.

Good luck with your new fish. I hope things go well.

 

[Fishperson]

If you want to stay updated on this tank please go to my thread "20 Gallon High Journal/Questions"