Another example of the deterioration of qualified people offering advice about pets.
I would certainly get in contact with the owner or manager of the store to let them know of what happened. Not to ask for a refund or exchange but to explain the situation to them and how it effected your view of his/her store for future purchases. ( A good store will offer you the refund or store credit without you asking.)
That's actually not 100% true. Not all stores are looking more at the sale than they are making a long term customer. The good stores are looking for customers more than sales because they know, over the long run, a long term customer will spend a lot more money than a quick 1 and done buyer. Here's a great way to weed out the bad stores: ask about buying something expensive that you know is not a good fit for your tank. The ones that say "Yes" are not good stores. The ones that say "No" are the ones you support with your business. They obviously have your long term business in mind.