Adding another clown

[qn5]

Hello,
I am thinking about adding another clown into my 20L. Currently, I have a juvenile clown which hosts frogspawn and a colony of red mushrooms. My clown has been alone in the tank for 3 months now. I was told to get a much smaller clown. This way, there won't be any aggression to the new comer. Are there anything else I should know before getting a new tank mate for my clown?
Thanks,

 

[xdave]

I would not get a much smaller clown, a little smaller or larger, but not a very different size. Definately the same species. There are many clowns with different attributes, please state the species.

 

[qn5]

thanks for your reply. I currently have a false Perc in 20L and He/she is about an inch or so. Also, he/she used to chase another Perc around the tank but the smaller one jumped out the tank 3 months ago.