20 Gallon Stocikng Question

[kiriyama]

Hi, looking to add a shell dweller to a 20 gallon/95ltr tank, current residents would be
1 Ancistrus
2 Julidochromis Dickfeldi
4 Alto. Comp. Shell
I will have Multis in the smaller tank..
Any suggestions on a small shell dweller that won't need a big territory and isn't overly aggressive ?
Any suggestions greatly received ......