The scale of your tank should be in your favor.
Getting fish to school (shoal) has been one of my pet peeves / Holy Grails for the past 6 years.
From watching and reading about other people's successes,
Scale is everything.
From the scale of the tank to the tiny shoaling fish.
To the scale of the 'Jerk' fish to the tiny shoaling fish. To the scale of the long branching open home area.
1. Minimum tank size seems to be 100 gallons. 200 is better. 300 is even better. 300 gallons seems to be the sweet spot from reading about other people's success stories.
2. The shoaling fish need to be small. 3" or less. They should also be young specimens.
3. They should have a 'jerk' fish that is noticeably larger than them that annoys them (without eating them). It gives them a 'outsider' to rally against and reduces internal hierarchy squabbles.
4. They should have a large home area of open long branching Staghorn or something similar that they can swim in/around and hide in and hang out in comfortably, without being stacked up against each other, like sleeping sheepshead stacked up against a concrete pile (whole 'nother story [emoji4]).
None of this is from personal experience. Just from reading about other people's success stories.
We are currently attempting a harem of 6 1" Royal Gramma in a 75 gallon tank.
The tank has almost 200 pounds of holey live rock in it for bolt holes and overhangs.
Plenty of different sized holes so the smallest can hide from the larger ones.
The 'Jerk' fish is just a pygmy angelfish, but it is doing its job well.
Everything is working so far, but it has only been three weeks so it is far too early to tell.
Look forward to hearing about your success with your Cardinals!
