I have a 20 high gallon tank. I have 3 zebra danio, 1 female and 1 male dwarf gourami. Now the problem is is that one day i noticed this black dot on the side of my tank. I looked closely at it and it was a snail and i dident put it in there. Im guessing it was atached to one of the plants i bought froms jacks. Now everyday i keep on see snails on the side of my tank and i flush them down the toilet but they keep on apparing. What should i do to get rid of every last snail.