Hello all, First time user here! Today we went canoeing in a freshwater pond and took home a couple empty snail shells. After rinsing one larger shell we put it in our freshwater tank. We have one clawed frog and one angel fish in our five gallon tank, and I'm worried the shell wasn't safe to add! My angel fish has been hanging out above it too. We were thinking it could be a nice addition but now I'm worried it will mess up their chemical balance! Does anyone know if this is safe for our tank? Should I remove it? Note: there is still pond algae on the shell.