If I were to try to "mate" a pair I would want at least a 46 gallon or larger , ideally Iwould want a 50 gallon tank for them. If you set up a larger tank for them then let it cycle. If you place them in at the same time you might be ok . For one maroon fish a 30 would be ok but pushing the limits imho.
You have a juvi clown now and they are less agressive the younger they are , so I would think that in my opinion you could do some rearrangeing of the rock work to confuse the current fish . When I add a fish to an already inhabited tank I do so at night , I will rearrange some rock work to confuse the territories up a bit , then drip acclimate the fish in a dark container ,to allow them not to be to stressed by shadows, after acclimation I place the fish in and the lights are out so the new fish is in the dark and allows them to find a place to go I have had very good luck adding fish this way , with minimal quarrals , I also try to get a smaller fish. Then I top off the lost water as it would be for an h20 change . Keep a container near buy and observe them to make sure they are playing nice and the 1st one doesnt get to agressive against the other one , some agression is normal if you see that there is a huge (frayed fins)problem take one out . One of the things that we also do is to remove the first one (about 2 hours will work for confusion that coupled with the moving rock work around will work well) rearrange rock work and place the new one in then place the 1st one back it will confuse them to bits .. place another slightly smaller maroon in that tank while the first one is out so he will be in the tank for a couple of hours before the first one is added back . For long term sucess (over a year) your tank is definatly too small for a pair of maroon clowns , the clown that we had (gold stripe) was a fast grower and they will grow noticeably in the first year with steady growth through out thier life, maroons potentially can grow up to 6.5 inches long , you could wait till summer and still place the new one in successfully , but it is easier when young . Oh and dont forget to qt your new fishies :mrgreen: Hope this helps