I rehomed my shark to someone with 125 gallons after it ate all my zebra danios. I don't recommend them in anything smaller than 75 gallons.
Craigy, you should up the existing schools of fish you have prior to purchasing another species. Go for 6 danios and 5 tetras.
75: blood parrots, featherfin cat, emperor tetras, turquoise rainbowfish, BN plecos, japanese trapdoor; 46: WCMM, gold inca snails, ghost, bamboo & amano shrimp, kuhli loaches, rummynose & ember tetras, endlers, platies, flame gourami, guppies; 16: pygmy, peppered, loxozonus corys, otos, assassins, RCS ... ~ Research PRIOR to purchase.... ~