I have had the same problem as you I think. Don't know if it is a problem but it sure it strange. One of my hitch-hiker snails (Not sure what its name is but it has a very thin shell, looks like a snail without a shell) He is usually nocturnal but was out during the day on the side of a rock where there was alot of current. He then proceded to spit or spew out brownish looking microbubbles. If they were baby snails, I'll be extremely happy but I think I only have him, no others. I wish I had an answer for you but I don't. Just want to let you know you aren't in this boat alone.