100L is 22g UK or 26.4g US.
How big are your clown loaches right now? Be aware that they grow far too big for your current tank. You will need to find a new home for them eventually.
Has your tank cycled yet?
Only if it has cycled, I would suggest a nice shoal of 6-8 peaceful schooling fish, like Rasboras or Danios. That would complete the tank nicely until the clowns outgrow the tank.