Bad health or bullying? Advice needed

[LeTigra]

Hi
I have an 80gal with Tiger Barbs, Pictus Cats, a Rainbow Shark, some Kuhlis, otos and a few Harlequin Rasbora.
A couple of months ago I noticed the edges of some of my Tigers' fins were looking a bit ragged. I had 17 of them at the time. I googled it and it looked like fin rot or maybe some fungus infection so I treated with a finrot/fungus medicine. I then did it again a couple of weeks later just to be sure.
I'm doing about 30% water changes maybe once a fortnight - I don't have a strict fert regime so I don't do huge water changes and the tank is understocked and has plants. I don't test - the tanks been set up for 18months in this new house and for over a year in my last house so it should all be stable. But I am down to 11 tigers. No-one else in my tank is suffering - being that I have ottos, I figure if there was a problem they'd let me know.
One of my remaining tigers now has ragged fins. It looks like he has holes in his anal fin right close to where it meets his body. Another has a fresh "hole" in its side that looks like someone's taken a chunk out of him. And ANOTHER looks like he's had most of his pectoral fins chewed off and he's just wagging stumps

I don't want a lecture on not testing - I'm not the only one. I'm just looking for advice. If my tank wasn't stable my ottos would be dead. If I had a serious finrot or fungal issue surely it would show up on other species in the tank, right? I suspect that by morning I'll be another tiger down - he's not coping well with a hole in his side although no-one is bothering him about it now.
Are they killing each other? When I had only two I had less problems!

[lauraleellbp]

How long did you have the Tigers before the issues started showing up? Were there any new fish added to the tank?

I suspect that the issue may be a combination of problems, but I'd definitely QT the fish that currently are showing symptoms. Bad thing about a large community tank is that problems can spread through large numbers of fish very quickly...

[kid creole]

Fortnight? Do you know Lancelot?

[plaakapong]

Keep an eye on the Shark! I won't have them(or tiger barbs for that matter) in my tanks for this reason. If it's not the barbs themselves I would suspect the shark.

[mistergreen]

it's probably both reasons.
they will bully sick fish, survival of the fittest and all.

[LeTigra]

Thanks guys for getting back to me

I don't get the Lancelot comment.... If its something derogatory, I'd really rather not know.

I have smaller tiger barbs that I got later than the others and they're fine. Its just the bigger ones that I've had for 8-10 months that seem to have a problem. Even the smaller ones I've had for about 7 months though, and I haven't added anything since then

A mystery. I'll up water changes and treat the whole tank for finrot and fungus again just in case. I just don't get how the only fish effected in my tank are the tigers. Even my ottos are fine

[kid creole]

Originally Posted by LeTigra

Thanks guys for getting back to me

I don't get the Lancelot comment.... If its something derogatory, I'd really rather not know.

I have smaller tiger barbs that I got later than the others and they're fine. Its just the bigger ones that I've had for 8-10 months that seem to have a problem. Even the smaller ones I've had for about 7 months though, and I haven't added anything since then

A mystery. I'll up water changes and treat the whole tank for finrot and fungus again just in case. I just don't get how the only fish effected in my tank are the tigers. Even my ottos are fine

In the US, a fortnight is not a term every body knows. The only time you might hear it is in a movie with knights, kings, and horses. Lighten up. Everybody is not out to get you.

[LeTigra]

Originally Posted by kid creole

In the US, a fortnight is not a term every body knows. The only time you might hear it is in a movie with knights, kings, and horses. Lighten up. Everybody is not out to get you.

Okay
For those who don't know what it is - a fortnight is two weeks

And yes, Lancelot is a very good friend of mine......

[kid creole]

Originally Posted by LeTigra

Okay
For those who don't know what it is - a fortnight is two weeks

And yes, Lancelot is a very good friend of mine......

OK. Now that we're on the same page, let's make some jokes about Welsh stereotypes. jk.

I'm stumped, but I lean towards this being a problem with fish agression/nipping, not fin rot, for the reasons you mention.

As far as testing goes, I don't do it either. Not because I'm lazy, but because I don't think they are worth a damn in my price range. With that said, if I was having trouble, I think I would take a water sample in to the fish shop. I could see this being a survival of the fittest situation, and the root cause is some other disease that is weakening the barbs.

Another thing that comes to mind is tank temperature. You didn't say what you keep it at, but it could be that your temp does not favor the barbs, weakens them, and exposes them to other fish who feel better.

[LeTigra]

Tank sits at 25 degrees C - I believe thats 78F

Good idea about taking a sample to a shop. I'll get that done, see if there's anything obviously problematic with the water