I have 5 mystery snails that I got a couple months ago. They are all in my heavily planted 20 gallon long tank along with 4 neon tetras and 5 amano shrimp and a couple of nerite snails. For the most part the snails are thriving, and I just got 3 egg sacs in the span on one week! They grew incredibly fast, and I feed them almost daily with algae wafers and spinach and cucumbers, and I add cuttlebone to the tank for extra calcium. I also do a weekly 20-30% water change. My only concern is that they often go up to the surface to breathe. I always thought this was a normal thing, but then I heard people saying that it means low oxygen levels. They do spend a lot of time roaming and they have good energy levels, but I often find them roaming then climbing to the surface to breathe, then going back down. Is it true that it's a bad sign if the snails come up to breathe, or is this normal behavior?