The micro stars that often make up part of a clean up crew will be just fine in an 8 gallon bio-cube. They will scavenge left over food and no special care needs to be provided for them.
Any of the larger starfish will likely just die of starvation as a small tank will not provide enough food for them long term.
I have 2 in my biocube 29, red brittle star and red sea star. The sea star is small only about 1-1/2" across. Been in there for 4 months now cleans everything i love it. The red brittle scavanges the live rock and i also give it some clams or squid every now and then, it loves them. Havent had any issues with anything yet and the brittle star is pretty large it has long tenticles.
IMO either one would do ok. you will need to feed the brittle more often, they hide alot and they do get large. The red sea star is my favorite, brilliant color red always out always somewhere new in the tank and it hasent grown much at all in almost 4 months.
can you post a pic of the star and provide some more info? I have always wanted a star but was under the impression that they will slowly starve to death in nano tanks and require alot of rockwork.
Well, i feed him frozen mysis shrimp, frozen larg shrimp the ones that humans eat i just rinse it with fresh water, live and frozen crabs, live snails, live hermits, frozen or live mussle, frozen squid, and live and frozen earth worms.
does he go after the cuc then? I have a few turbo and astrea snails and do not want them to become dinner. Any pics of the star. I did not see him in that pic with the puffer.