Help with possible fin-rot and other problems.

[Kyshiara]

Hello! I have been on holiday for 5 days, and I got back and found that my Zebra Danio's tails are slightly ragged and milky-edged. I recognise this as fin rot.There are only 3 of them (there were more, they died) and my LFS was suggesting this:

I currently have my four Panda Corydoras in quarantine, as they had the same problem. I treated them with fin-rot treatment, and their problem has now cleared up almost completely while I was away.
My LFS was suggesting that I moved the Corydoras over into my main tank again when that fin-rot cleared up completely. I am planning to do this.
They then said to leave it for a couple of weeks (as in not doing any water changes, adding or removing plants/fish etc.) and then get some more Danios.

They were suggesting to get more because I had a Sparkling Gourami (died while I was on holiday- I don't like going on holiday for this reason) whose tail had been bitten off completely. I moved it into the quarantine tank, but it died after 2 weeks I think. They thought that having more would mean that the aggresion was spread between them, and only them.

I also think I need another couple of Sparkling Gourami as I only have one now.

What do people think?

Thanks!

 

[Kyshiara]

Tank size: 60l
I will get the parameters if you need, but I have had the tank for 2 years and the water has ALWAYS been fine. And that's when the problems were. And the water was fine. So it's not the water.
I can also get pictures of the tank and possibly the fish, but you know Danios. They are quick little pests. (I do love them though)

 

[Colin_T]

pictures of the fish and what's the question?