A LFS worth its weight in salt (pun intended) should take back a fish that it sold you if it's not working out. Even if they don't give you a refund or store credit, they should take it. At least that was my experience when I lived near a LFS (I don't now--everything I get has to be via online vendor or from another local aquarist...or drive 100 miles to a not-so-local store). They should be incentivized to at least give you store credit (even if only partial) because they want repeat business. In any case, that would be my first attempt if I were in your shoes: Talk to the LFS and ask them to take it back. Again, even if they give you nothing in return (which would indicate maybe stop patronizing them), at least you solve what is an untenable situation as there isn't a scenario where that fish thrives in that small of a tank--it may even not survive as it grows as it may start thrashing into rocks as it gets more cramped (that was why I had to rehome my batfish years ago--it was beating the crap out of itself by panicking and smashing into rocks--and that was in an 8 foot 375 gallon tank).