It seems all to familiar, my fiancée had the same idea once she saw me setting up my tank ... Lol .... "oh I want one too "... Poooof! their goes another couple hundred bucks for mr seahorse and his friend... so twenty seven seconds ago. Anyhow back to your thread.
In 30 gallon... a pair would do just fine, I have a pair on a 20 gal with a whisper HOB filter rated at 30-50gal and they seem to be perfect. I might move them to a 40gal i have in storage but thats another project. I also have one live rock and a sponge in with them. Nothing else but the circulation of the filter works for me. I don't have any circulation pumps or jets which means I have to keep algea in check and also monitor phosphate levels and feeding volume. Best of luck!