I had a bta in my 30g tank with no issues. But 2 points, 1) your tank is how old? It needs to be fairly mature to keep a bta, especially given the small size. 2) your water parameters need to be stable and kept that way. Other points, you will probably need to feed it every 2 to 4 weeks since your tank is small and don't be surprised if it moves around in the tank. Anemones rarely stay where you place them as they have a mind of their own... they are the cats of the aquarium hobby.