I have 6 serpae tetras, few of them have one large white spot that is more developed than others.My tank:140 liters, well planted, i change 25% of the water each week, i have nasty infestation of some little brown snails(planorbis or something), i have 1 little bristlenose, 3 corys, 6 serpae tetras, 1 angelfish 2 pseudogastromyzons, i have 1 internal filter(300 liters per hour) 1 sponge filter & 1 air stone. That's basically everything. Here's some pictures.