[BoomerD]

Anthony Calfo says one sand-sifting star per 200 gallons, and only then, if there is LOTS of open space between the rocks. These stars live by eating the "bugs" that make live sand "live", and in a small tank, all too often, they decimate the life in the sandbed, then starve. Not sure what your "red seastar" might actually be, since there are many stars that are red...but most will quickly outgrow a 24 gallon tank...