They most likely wont get much bigger if they're what I have. The look like a tiny ramshorn but the shell is sideways (flat to the glass rather than sticking out) and they never get larger than a few millimeters across. I have lots of these little golden tan snails that just "appeared" in one tank and then migrated to other tanks as I did tank maintenance. I think they must have come in on one of my plant purchases. For the most part I don't mind them as they don't harm plants.