I've had my sand sifting star in my 75 gallon for over a year and fine for the last 6 months in my 230 gallon no issues and both tanks where new when he arrived
Sand wasn't new though, basicly the star lived in a system with a new sandbed, and then was moved into another system with a renewed supply of sand full of food.
One thing alot of people misunderstand when it comes to stars like these, is that results aren't overnight. Countless threads have I went on and on about the survival ratio of these species, however truth be told I myself had Fromias for 6 months before the clock stopped ticking. Any future atempts, all dead withen the month.
Why is this? Well, when a starfish is going through starvation, we think just suddenly it's going to croak the same week of addition.. however, the symptoms can be very silent and the whole process span out for a very long period of time.
Even if the star is out of food.. there is always that tinnie tiny trace of food during the starvation period. It's like having your fridge being empy.. then every day you find 5 grapes and live on those.. you're not going to die as fast as you would completely without food of course.
With stars this is the same case, food become scarce and difficult for the animal to find at a certain point, eventually they begin starving, but find those little grapes to keep them going another week, then they find a tiny bit another week, and this can go on for the following months or years until their stomaches begin to reject food, which leads to what this person here is experiencing.. the melting process, aka death.
Basically, your starfish may looks like it's doing fine just because you've had it for a year, however in reality, it's going through a very slow starvation period which you are unable to detect until it finally dies, which can be in the near future or early on.. or even from another cause like water quality swinging or something. This is especially noticable in the replacements, when the replacements starve much faster since the previous specimen/s already took their tool on the food supply.