Fin nipping cardinals

[Alien Anna]

I've been treating my tank with Melafix for what I thought was a mild case of fin-rot. One fish recovered completely, but another seems as bad, if not worse than before.

He is very old. He's a 6 year old cardinal tetra (I'm told by the previous owner), so it doesn't surprise me that his health isn't so good, but today I noticed him being harassed by other cardinals and I realised his fins are actually being nipped rather than infected. He's swimming about well, eating and his colour's good, and I know he's not got long for this world, but how can I prevent him being bitten to death?

Would it help if I had a bigger school? I have five cardinals, of whom 3 are equally old. I don't know the sex ratio. I have thinned out out the population of that tank recently, but I don't know if it will help or hurt this problem.

He's also with 6 rummy-nosed tetras, 5 cherry barbs (not fin-nippers, btw), 4 gouramis, 2 pencilfish and a bristle-nosed pl*co. The tank is 110L, mature and heavily planted. pH 7.0-7.5, KH 6, GH 10, nitrate <10, nitrite and ammonia 0.

 

[pete]

A larger shoal may well help due to there being more Cardinals to even out aggression :what:

Give it a try and let us know what happens

 

[Davy Reynolds]

It might go the other way. An injured old fish may be at the old of the road and the others know it and this is why they may be picking on him :what:

 

[Feargal]

I agree with Davy, if the Cardinal is weak and old it makes it an easy target and the others will have a go.

I'm afraid that in the fishy world it may be a case of only the strong survive.