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4" is an adult for that species. Its also wild caught since you got it from what sounds like a chain store, which means you'll never know its age. It could easily be 10 years old. Could be 5. But at 4" it is definitely several years old.
Take the moss out. Its not necessary, unless you keep the moss absolutely dry its more for a visual thing. 30 gal is infinitely too big. A full grown rosea could live in a 5gal comfortably, but 10gal isn't bad. When you say chips, what do you mean by that? To reinforce why a 30g is a terrible...