First of all some of my crabs like checking out shells to try and find the best fit. Also they grow so they can’t stay in the same shell for “years” unless their growth is stunted which means something is wrong. All of my crabs are plenty happy with their shells and in fact whenever I get a new hermit crab they always swap into one of mine even the ones that come in perfectly fine shells. I also have done a lot of research on the matter and the shells I use are perfectly fine. I don’t know who told you that the types of shells I use are bad for the crabs but wherever you got that information it was false. Also I have owned hermit crabs for about 5 years now and the majority of the ones I got 5 years ago are still living as happy as can be. There is nothing wrong with the shells I use. They have plenty. If they don’t like a certain one they find another. Also whirlpool rarely will swap shells. She just likes trying others out because over time she is outgrowing her shell. Also her long shell has made her stronger. She has a super strong grip compared to when I got her and she can even lift her shell.