It will only make a mess in the tank if you don't clean it up lol my advice is spend as much time as you can infront of your tank as this will help them get familar with you and less panicked when somebody walks by get them on pellets at an early age and keep they tank clean as for tank mates when they get to adult size neons they don't usualy bother as imo they expend more energy eating one than they gain plecos work as well as some armord catfish