Best way to add fish to betta tank

[DogFish]

I a few weeks I will be adding some harlequin rasboras to Flame's 10 gallon tank. Since some bettas are agressive toward other fish, and Flame will feel like he owns this tank, is there a "best" way to add these new guys?. The tank is well planted, so there will be hiding places.
Should I stick a divider in for a few days? Keep flame off to one side?

 

[Carolinesugar]

hmm, u cud try rearranging the whole tank the day u get the harlequins. just make sure u do it say abt half an hour b4 u go and get the harlequins, or flame will assume its all 4 his benefit.

how long has flames tank been running for ? as harlequins are very strange fish - i have them. if the tank hasnt been set up 4 at least 5 months, they seem to die, or just kill each other. ideally they like to be kept in schools of 6 or 8.

other than being abit strange with the way they seem to drop dead if the water and tank hasnt been set up for a long time, their great lil fish. but ur have to make sure u kept a hood on the tank, as their norty lil fish, and like to jump out!

good luck getting flame settled and accepting the harlequins.