I have 2 female puffers (I think) and one (seen at the top of the photo) just always seems to be skinny looking and almost anorexic at times. They dont seem to have a bully situation and the skinny one is always first to have its fill when I feed them! I've even tried feeding multiple times through the day. I just always feel bad like she's hungry and I need to feed her I even have pest snails that reproduce in another little tank to give them as treats but she never puts on weight? Any ideas?