Funny, others would say stay away from any brittlestars, because they will be predatory and serpents won't. Really, there is absolutely no way to make this generalization at all.
The green brittle is a known predator in the wild. Others may or may not be, we just don't know. And that behavior may be totally different in a tank. There are no guarantees. It is an individual personality issue.
Any other brittlestar or serpentstar is a good choice, however, when adding any animal to your tank, you need to accept that it may eat something. They must also be spot fed, and not allowed simply to scavenge.
I recommend you let your tank mature further before adding any type of echinoderm. Also, specific gravity should be 1.025-1.026. They are extremely intollerant of ph, salinity, alk, etc, fluctuations.
A long drip acclimation, at least 4 hours long, is recommended.
Other reef safe stars area available, however, your tank should be no younger than 6 months old. Tank conditions should be pristine. It should also have a lot of LR, at least 75-100lbs for best success. Reef safe stars feed only on LR and can not be spot fed. They commonly die of acclimation stress within a month, or at about 9-12 months of starvation. Only one should be kept in most cases, unless the tank is very large. The exception is Linckia multiflora, which does well in smaller tanks. Other Linckia and Fromia stars are much more delicate, and much more prone to starvation, regardless of how small they are.
They also require very long acclimations. There is a lot of info that you can search for. I can also send a link to you if you wish. You can contact me at
ophiuroid@att.net
I also do not recommend a sand sifter star if you want a functional DSB, though others may disagree. It is another animal that often starves at about 9-12 months.