You can choose any other Ocellaris type of clownfish they will pair up as long as the new addition you are pairing is smaller than the one you are pairing it with. Also if you choose a smaller Ocellaris make sure it is in a tank of multiple clowns. A clown on its own can very quickly become a female and then pairing the two would be impossible. I'd suggest using an acclimation box also, but may not be necessary. I paired a large maroon Goldstripe with a very small Goldnugget juvenile and the pairing went perfectly with maybe only 2 hours in a Kritter Keeper box next to her RBTA. Ocellaris are far easier to pair.