Relax a little while. Some times it takes a bit to make a new house feel like home. If that's the only symptoms maybe he's just getting use to it all. If you really feel like he's uncomfortable with his new home give him a plant or two. A water plant from the pet store can be placed in a terra cotta or plastic container and put inside his tank if you don't have gravel. Now you didn't mention filteration or what size tank. If this is a totaly new tank gravel and all, your tank may just be cycling. If this is just a larger betta bowl he may just be producing an excess of slime coat due to stress. If there are other symptoms making you think he's sick or you need more advice, write back and tell us more
Carol
larantrow