hey guys! so im new to the hobby, and i need some help with things i can put in my tank. the other day i went to Walmart,and in their craft section i found a bag of shells. they would look great in my tan. however, i know that your suposed to be cautious about what you put in your tank. could i clean them? they are in this huge bag in the flower department. just let me know what you think! thanks so much!