need some advice, new to forum, but i have a 6 gallon wall salt water tank. when i originally set it up, it had peppermint shrimp and lots of hermit crabs. they all slowly died. i figured it was their time. since then a couple months apart, i have tried to introduce new shrimp and crabs which have all died within 24 hours. i have acclimated them properly. also have had some snails die but some live, recently a conch and peppermint shrimp died within 24 hours but several other snails and 3 fish lived that were added at the same time. i had my water checked and he said it was perfect. thank you for any advice!