What size tank ?
Rosy Loaches are tiny and cute. My friend has a big group in a 20 Long.
Dwarf Chain as was mentioned, but they are little hoodlums, so you need a big group and tank mates that tolerate their antics.
There are so many Cory species that you could have a diff species in each tank ?
Clown Loaches are awesome for giant tanks.
I loved my Eels and my Elephant Nose that I had in my big tanks in the past.
Zebra Otos are great looking, but more pricey and sensitive. But once established in a clean well planted 30g or larger a group of them is very attractive.
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