Topping Up A Shoal

Just wanted to hear some opinions about adding a small number of fish to an existing shoal.

As some if you will remember, I lost a Green Tiger Barb recently, so want to replace him.

I bought six Otos a while ago, one died a day or so after being transferred from the QT tank and two disappeared, so I want to get three more to bring the shoal back up to six.

I've just had a Cardinal Tetra die in mysterious circumstances, the day before yesterday he was fine and then yesterday he was bloated and unable to swim properly. He died shortly afterwards.

Incidentally, yesterday I also noticed a one-eyed Cardinal but he looked otherwise healthy.

Anyway, back to the query:
I want to add a Green Tiger, three Otos and a couple of Cardinal Tetras to the community.

However, I'm concerned about keeping shoaling fish in relative isolation in the Quarantine Tank.

Bearing in mind they're only going to be in the QT for a few weeks, perhaps it won't be such a problem?

Or maybe the whole idea is ill-advised and I should wait until I need to add more of the same species.

I'd appreciate opinions, how have others handled a similar situation in the past?

Thanks Sue.

I had considered the hierarchy issue as the Tiger Barbs frequently have little battles to establish their pecking order.

I originally had six standard Tigers and after a few weeks added the six green Tigers. The green ones were far younger and smaller and they didn't fight and the standard Tigers didn't compete with them. Thankfully they just merged into the shoal with no issues. They're as big as the standard Tigers now and they all squabble but it's playful rather than violent.

I'm hoping that if I add another juvenile green Tiger they'll allow him to join the shoal.

I'll probably end up getting these fish as exchange for my juvenile Apistos, so should be putting these into the QT in a couple of weeks.

I'd be a little worried putting 1 tiger barb in quarantine with the otos and cardinals. They display aggression on their own I believe.

I'll keep a close eye on things in case there's any shenanigans.

Sneaky little buggers those shenanigans, turn your back for 5 secs and .........

  lol.