Schooling catfish?

[J. H.]

The Brochis species look like giant cories, aren't to expensive, shoal really tightly, and when I had them, where Hardy, long lived and super active. Mine only got about 4", so a bit smaller than what you want, but you could get a big school, and they are quite chunky, so they might fit in with your plans for the rest of the tank.

 

[J. H.]

The Brochis species look like giant cories, aren't to expensive, shoal really tightly, and when I had them, where Hardy, long lived and super active. Mine only got about 4", so a bit smaller than what you want, but you could get a big school, and they are quite chunky, so they might fit in with your plans for the rest of the tank.

I see people online selling them for upwards of $30! I got mine for $5/ea. ~7yrs. ago. I see some people selling some species at $4-10, though.