The tank is about 6 months old
Welcome to Reef2Reef! You'll love it here!
I'll start by asking how old your tank is. Majority of sea stars sift through the sandbed and eat microorganisms such as copepods, which new tanks have a very little amount of. Mature tanks are often better for starfish simply because any food populations take time to establish. Chocolate chip stars, like any star, will always benefit from being fed meaty foods. Without proper food, stars slowly deteriorate and perish.
Starfish are also extremely sensitive creatures. They need perfect and stable parameters. In a new tank, this is hard to achieve. Could you post your ammonia, nitrates, etc.?
How did you acclimate the star? Many reefers lose their starfish due to poor acclimation.
In short, starfish unfortunately don't survive long in new reefs, and require a certain amount of care and expertise to thrive. I believe any one of the above reasons could be why your starfish is doing poorly, but hopefully things turn around for it.
And I will recheck everything tonight and let you know the levels
And I explained all of this to the pet store prior to purchasing and they said he would be just fine