IMO, do not use seastars for this purpose.
Certainly none of the "reef safe stars" such as Linckia or Fromia are suitable for this system.
Seastars are really not cleaners. Certain brittlestars may help clean up left over food (avoid the green) but they should be spot fed and are not guaranteed to "clean". Many will not consume detritus and you must address that problem in other ways.
The small hitch hiker Asterina spend more time on hard surfaces - they may not eat extra food. The hitch hiker brittlestars may be a better choice.
Your left over food and detritus are an indication of overfeeding, so I would just address this directly, personally, rather than try and find a seastar that will address this (they really won't).