I have a question... I really want some frogspawns, but I'm not sure I should mix them with the ritteri anenomes?

I'm thinking if I have a 55 gallon or higher tank I can easily keep them apart.. but what about a 20 gallon long? I know I know it's too small for a ritteri, but I plan on starting small and when it grows too big I'll move it in the future.