Are you sure it was an astrea because they only get around 1 inch - just asking. I had 5 die right after I put them in and nothing happened to my readings. I had acclimated them for 2 hours before putting them in, they never moved and I know they were in the shell. The next morning they still didn't move so in the afternoon I started picking up any that wasn't moving, they had already been cleaned out. I guess my cleanup crew did a good job. Not sure what happened but all the others did just fine and my reading never changed. I even purchased another test kit just to be sure - nothing. It looks like your tank is going through it cycle so things should get back to normal. You might want to really watch your other snails because I don't think they tolerate high nitrates at all. Good luck.
