Red sores turned white; injury or disease?

I have a Diamond tetra that developed a red sore at the base of his tail fin near the top of the fin (make sense?) that has now turned to white with the top portion of the tail fin missing. I noticed this Tuesday night as I was feeding the plecos right before lights out. I checked Wed morning when feeding the other fish (tank setup below) and it was no longer red, but it was white. I checked again when I came home and before I went to bed, and it looked the same. I checked this morning, and now there is a similar bump at the bottom of the tail fin. It has a white center with surrounding white. When I get home tonight, I am going to set up the QT tank using media from this tank (biofoam from the Whisper filter) and start dosing with Pimafix. Otherwise, he seems perfectly healthy. He is eating and swimming just fine and acting normally.

I had also had one of my other Diamonds just suddenly die. It was fine the night before (Monday), and when I fed them Tuesday morning it was dead. Coincidentally, it was in the dwarf sag and moss right where the kribs have been guarding their babies. I did not see any evidence of wounds, though, and I could not identify a disease. It was fine the night before but dead during the night!

Now, for the tank mates and politics, lol. I had 19 diamond tetras, now only 18 since the one died Monday night. I also have 6 kribs. There are 2 pairs and 2 extra females. I have been meaning to arrange with the LFS to sell 4 leaving only 1 pair, but other things have come up and I have not gotten there yet. Also, one lfs said I'd have to bring them in and check out how they look, etc. before they agree to buy them. I was not about to put them through the stress of netting them, bagging them, driving 30-45 minutes, waiting for them to inspect them, and then maybe even having to bring them all the way back home!

Anyway, I also have 2 honey gouramis, 2 L387 plecos, 1 tiny gold ram, and maybe 20 or so guppy/Endler mixes. I also have 8 nerites (olives and C. corona), a few common ramshorns and pond snails, and many, many MTS.

Oh, yeah, I mentioned the kribs guarding babies. They had a batch a little over a month ago, which all died in the first 3 days. Not sure if others ate them or if they got sucked into the filter. I since have covered the filter intakes with sponges, and they had another batch. They started coming out of the cave about 1-1/2 weeks ago, and there are about 30 of them, plus or minus. The parents have been chasing everything away, but they mostly seem to be chasing, quickly darting at the other fish and then quickly going back to the babies. I don't see any real fighting, but I don't know what's happening while I'm at work or after dark. It's entirely possible that they are, indeed, being more aggressive than I have seen so far.

Tank basics: 75g community with Marineland C360 canister and Tetra Whisper HOB with sponges only. Heavy emphasis on biomedia. Temp is 78/79 F with 3 200w heaters (house tends to be cold 'cause of hubby). Lighting: Coralife Single Compact Fluorescent; no sunlight exposure. Lights on for 10 total hours a day split between morning and afternoon/evening so that I can have the lights on when I'm home.

Test results from Red Sea kit: Ammonia 0, nitrite 0, pH about 7 (maybe a little less). I don't currently have a nitrate tester.

Fairly well planted with anubias, Java moss and fern, bacopa monnieri, water sprite (planted and floating), some najas grass, dwarf sag, pennywort, salvinia minima, duckweed, and water lettuce. Can't think of anything else, but might be missing something. I dose with Excel every other day. Had also been dosing Flourish Trace but ran out about a week ago.

Hmm, anything else? Sorry to be so long winded! I am reconsidering keeping the pairs and instead maybe keeping the 2 females that are unmated. I'm not sure, and my decision may be based on what you guys think the source of the wounds are. I am really thinking that it is the kribs, but I have little experience with disease. My only other fish to get sick were a betta with fin rot from the store and wild-caught figure 8 puffers with internal parasites.

I'll try to get a pic, but they never stay still long enough to get a decent one.

I try to do weekly 50% water changes, but lately it's been hit & miss. I know, bad girl. The last one was 2 weeks ago. I'm pricing pythons and similar water changers. I'm leaning toward Aqueon, but that's beside the point.

No other fish are showing any signs of similar sores, or anything abnormal. They are all acting normally and eating normally, even the one with the sores.

If this is an injury rather than disease, do you think Pimafix would be a good choice? I have a small bottle on hand, but I could grab Melafix or a general cure type med if that would be more effective. Also, I think it would be better to QT him at this point since I'm not sure what I've got, but should others start developing similar sores, should I QT them also or treat the whole tank?

The plecos stay in their caves until after dark, so I'm not fully certain that they do not have sores.

Btw, the QT tank is 16g.

Thanks! Yeah, my first post is pretty windy, but I did mention that he wasn't in QT. I will set it up tonight and use the biofoam from the HOB in the QT filter to jump start it. I'll also try to do a WC on the main tank tonight. If not, Fridays are my WC night anyway.

I will update tomorrow and hopefully have pics if possible.

Btw, I have Jungle Lab's Fungus Eliminator from last fall for betta's advanced fin rot, and Ipicked up Gel-Tek's Ultra Cure or whatever it's called for internal and external bacterial infections, just in case.

Depending on how it looks tonight, I might dose the Pimafix.

I think I figured it out. I watched them for a while on Saturday, and I realized that, while most of hte time the kribs just dart towards the other fish and scare them away, sometimes the another fish will obliviously get close while the krib is scaring the main group away. Therefore, the krib then actually hits or bites the fish that got too close.

Also, I realized that both mated pairs have fry! So, the other fish are getting it from both sides. The mated pairs chose caves on either side of the tank, so there is only neutral territory in the middle towards the top of the tank. Even then, though, the kribs may still chase them as the fry are getting more adventurous. As soon as possible, I will be selling the mated pairs to the LFS.

I realized all this after I saw another tetra with a spot that looked like a bruise. The spot I mentioned in the earlier post at the bottom of the first tetra's fin had also resolved into a spot looking like a bruise. That made me think more like it was an injury. I watched them Saturday and Sunday, and the behavior of all the fish, especially the kribs, indicated that the kribs were being too aggressive. So, I'm gonna keep the 2 unmated females since they are not aggressive 'cause they ain't got no babies! Anyway, thanks for letting me freak out for a couple days, lol.

Oh, and I did get pics. They are crappy, and all you can really see is that part of the fin is missing. I forgot the jump drive at home, so I can't post them today.

I'll post pics tomorrow, unless I forget again. I am so scatterbrained these days.

But, after observing them all weekend, the one that had the original sores is looking better. You can hardly tell that there is anything wrong with it except for some missing fin. It is still acting normally. All the fish seem somewhat stressed from getting chased on both sides, but otherwise, they are all swimming fine, eating fine, etc.

I am about 90% certain that it is just injuries, and I will try to step up my WCs to twice a week until they are healed. If I can catch one pair, I am going to put them into the QT tank to reduce stress since I can't get to the LFS until Saturday. I am not concerned about the fry, since I don't want to deal with raising them. I just don't have the time or space to raise them. I wish I did, but... I don't know why I didn't listen to people when they said that having a mated pair in a community tank could be trouble. :wall: I am such a stubborn idiot!

Once again, I forgot the pics. Well, now I am certain that it was injury from the kribs' bullying. Last night I found one of my tetras was upside down, could not swim, and its fins were ragged. It was clearly not a disease process but actually beaten up by another fish. I was so upset! I had to euthanize it since it was completely unable to do anything but breathe.

Anyway, I moved one male to a different tank, and I tried to catch the other, but he was too sneaky. I rearranged the tank also, so hopefully that will help give them more of a place to hide. I was so mad that I was tempted to use the clove oil on the krib parents too! But, I restrained myself and remembered that they are just being good parents. It's not their fault that I stupidly put them in a position where they felt they had to defend their babies. I'm not sure yet if I will just sell the males and keep the 4 females or just sell the pairs and keep the 2 unmated females. My lfs won't keep the mated pairs together anyway, and I don't have time to sell them as pairs online. I need to get them separated asap.

On the plus side, the one that was originally injured is looking pretty good. It'll take some time to regrow that missing bit of fin, but at least he's swimming and eating and moving okay.

God, if only I had listened to all the people who had said it wasn't a good idea to put a breeding pair in a community tank! Maybe I should write an article for newbs... might help someone make a better decision.