Cardinal Tetra With White Mark At Base Of Dorsal Fin

[Hathaway]

1. Water parameters. (ammonia 0, nitrate approx. 50, nitrite 0, PH 7.8, temp 25c, Hardness 6.5kh)
2. White mark at the base of its dorsal fin. Otherwise seems fine.
3. 25% weekly water changes. Last one on Sunday.
4. Just seachem prime and flourish after water change as far as chemicals go.
5. 1 opaline gourami and 9 black ruby barbs, all juveniles added 3 weeks ago and healthy. 7 other cardinals, added at the same time.
6. 4 foot 350 litre tank.
7. Cardinals were added on Monday, no other fish added.

So one of my cardinals is showing a white mark at the bar of its dorsal fin and I'm concerned that if it's a problem then it may infect the others. So I don't know what to do. Do I medicate the tank or remove him before he infects others?

I got them on Monday from what I hear is a reputable lfs (maidenhead aquatics), though I guess problems can occur anywhere. Another one is missing but could be hiding. He has plenty of places to go.
I had one mysteriously die on the first night, not sure why. He just became unresponsive and I isolated him to stop others picking at him, but he died later on. Another died on entry to the tank. I didn't see it but I think the gourami mistook him for food and broke its tail and it died instantly. She's shown some light aggression to them but has settled down as time has gone on. The barbs take no notice.

I appreciate any help that can be given.

 

[Hathaway]

Well I went back to maidenhead and bought some medication (aqua care anti-ulcer and finrot) that was suggested. I did notice later before leaving that his fin did look a little worse for wear.
Unfortunately when I got home I found a cardinal lying on the bottom breathing heavily. I carefully scooped him up but he didn't respond at all and has now died. The other tetra look fine so far, though I'm now down to 6. The other is still missing, which causes me concern, but my tank has so many places to hide I'd have to demolish the tank practically to look everywhere, potentially causing a lot of stress.
I'm beginning to think the stress of the gourami caused these fragile little things more stress than they could handle. She is fine with them now but perhaps the initial stress had already done its damage?

I had planned on getting a lot more for a large school but I feel like I need a better strategy for next time. Any suggestions here would also be appreciated.

 

[Byron]

I will not guess on the photo issue, but I may be able to offer some help elsewhere.
 
First, the opaline gourami is not a good tank companion for such small fish.  The species is Trichopodus trichopterus, and there are several varieties (blue, gold, opaline, 3-spot, cosby, marbled) which are the same original species which means they will have the same traits/behaviours.  This fish can attain 6 inches, though 4-5 inches in an aquarium is usual.  However, it is one of the more aggressively-minded of the gourami.  I have watched two of these gourami easily corner and devour a medium-sized neon tetra in a store tank.  I would not recommend this gourami with any small linear-shaped fish, so if you want cardinals I would remove the gourami.  However, I will come back to this.
 
Second, nitrates at 50, if this is in ppm (parts per million) is high for fish.  Is this nitrate in your source water (have you tested the tap water on its own?) or occurring in the aquarium?  If the latter, this should easily be rectified by more substantial water changes, not overstocking fish [from the tank size and fish numbers this should not be part of the problem], and not overfeeding.  Live plants, even if some floating, will also help.
 
As for the other numbers, the pH is on the high side for cardinals, but of more importance is the general hardness (GH).  You give 6.5 kh which I assume is KH, Alkalinity or carbonate hardness, which is related.  But do you know the GH of the tap water?  And what measurement unit is this 6.5?
 
Returning to the fish stocking, I would not add cardinal tetra to this tank with black ruby barbs (or the opaline gourami as I mentioned above).  These barbs, like most species of barb, are very active fish.  The cardinal tetra are the opposite, being sedate.  The two do not mix well.  Gourami are also sedate, and active fish do not make good tankmates for them either, but ironically here you have a rather feisty gourami that might manage better than many other species ever would.  But if the barbs are staying, then any future fish additions will have to be carefully selected from the more active fish.  I have a group of 18 of these barbs in my 90g (340 litre) tank, and they are in with a group of five kubotai loaches (Botia kubotai) which are also on the active side, and a group of 8 Congo Tetra which though not as active a species, do get racing now and them, and this has worked fairly well for a couple years now.  However, I would not add gourami to this mix, so this opaline has to be well considered too.  The similarity between the Congo Tetra and Opaline gourami might spell trouble.
 
Another point that may relate to the demise of so many of the cardinals is how you introduced them.  These are delicate fish, as are most of the characins.  But even beyond this, going into a tank with a "bully" like the opaline--and I would certainly characterise any individual of this species as a bully--only added to the stress.
 
Byron.

 

[Hathaway]

Another cardinal is showing the same signs. Could this be Columnaris? Is a white patch shaped like a saddle. I don't hold much hope for the guy but I need to stop this. My gourami has also become lethargic and I believe is constipated with a white spot on top of her head. I don't know if it's related or not.
Can I please get some guidance on this issue.

Is it worth using the Aqua care anti-ulcer and finrot medication I bought?

 

[Hathaway]

Those photos were taken last night. I've found her dead this morning. I'm concerned I'm going to lose the rest of the tetra at this rate. The barbs seem fine but may not be. I'm googling frantically but finding no definitive help, or meds that I can get hold of.

 

[Byron]

I am not ignoring you, but my experience with disease is very limited, and guessing as to what a disease may be can be risky.  Medications do impact fish, and when they are not the right ones, things can quickly get much worse.  So I will hope that some other members with more experience can help here.  I have dealt with columnaris once, some two years ago, but it looked much different from these photos.
 
Byron.

 

[Hathaway]

It seems to also compare with symptoms of neon tetra disease, the so called white saddle around the dorsal fin being a commonly seen symptom.
Another cardinal has died, others seem fine but that's no indication as yet.

I won't be adding any fish until this has long been resolved. Quite upset about losing the gourami. Setting up a quarantine tank may not be an option with the space I have at home unfortunately.

My previous responses weren't directed at you Byron but anyone who may have info. Though I agree that the guessing game may make things worse, so I've resisted temptation to just try medicating with "something".

 

[Byron]

It seems to also compare with symptoms of neon tetra disease, the so called white saddle around the dorsal fin being a commonly seen symptom.
Another cardinal has died, others seem fine but that's no indication as yet.

I won't be adding any fish until this has long been resolved. Quite upset about losing the gourami. Setting up a quarantine tank may not be an option with the space I have at home unfortunately.

My previous responses weren't directed at you Byron but anyone who may have info. Though I agree that the guessing game may make things worse, so I've resisted temptation to just try medicating with "something".

 
No problem, I just wanted you to know that I wasn't ignoring the problem.
 
If the cardinals go like this, it is possible they brought something with them, and it would be useful to see if the fish left in that store have been similarly affected.  They should credit you for the fish if they were the carriers and died so quickly after purchase.
 
More frequent partial water changes often help in any disease issue, though here I certainly don't suggest it will cure things.  But in general, if I detect a problem, my first act is to do a good water change, and test the tank water prior for ammonia, nitrite, nitrate and pH.  These tests can sometimes show up something, though again with what you describe it is less likely.  But still worth testing, just in case.  I don't see any external signs on the gourami in the photos, but a rise in ammonia or nitrite could be part of it.

 

[Hathaway]

Well I went back to the store a couple of days after to seek some advice and they all seemed fine at the time.
I have contacted them via their website to explain the situation, as the only store assistant there at the time gave me an inclination he wasn't really all that knowledgeable... though was quite happy to sell me some medication.
It's just left me now very nervous about the process of introducing any new fish. I may not see them quite on the same level as my dog but I do still get very attached, and being new to the hobby I don't relish it at the moment being about consistently looking for illness symptoms, counting fish and removing dead bodies.

 

[Byron]

Well I went back to the store a couple of days after to seek some advice and they all seemed fine at the time.
I have contacted them via their website to explain the situation, as the only store assistant there at the time gave me an inclination he wasn't really all that knowledgeable... though was quite happy to sell me some medication.
It's just left me now very nervous about the process of introducing any new fish. I may not see them quite on the same level as my dog but I do still get very attached, and being new to the hobby I don't relish it at the moment being about consistently looking for illness symptoms, counting fish and removing dead bodies.

 
I forgot previously to say you are certainly correct to not add any new fish until this is well resolved.  But I leave the diagnosis to the more experienced members.
 
It is indeed disheartening to have fish dying in this fashion, and feel powerless to do anything--which is when the temptation to add something is so strong.  Resist.  And be vigilant; it would be terrible if the existing fish (black ruby barbs) came down with this.