My apple snail was fine until this morning when he dropped of the glass twice and no longer grazes on the glass. He closes his mouth when on the glass now. He also has stopped eating. He rarely comes outa his shell. I feed him crab pellets cos of the calcium. Is that OK? He also keeps half of his foot off of the surface sometimes. All the nerites are fine. Please help! Ive only had him for four days. 