I seem to be having problems with my snails, in the past week I had two Conch's die and yesterday I bought 2 astrea's and 2 Margarita's. 1 astrea and 1 margarita made their way to the top of the tank glass and are almost completely out of the water (is this normal?). I checked my water a day ago and everything was fine. The only problem was my Nitrates were at around 15-20 ppm. Thanks.