Brennos, I also lost a couple of male guppies and about 5 Sunset WCMM the week before Christmas, central Auckland area. All water tests were normal, it did appear there was bacterial type infection. LFS sold me an AquaOne BioPet product which worked, along with a capful of colloidal silver daily, for a week. Small well planted tank, 38L. Sunset minnows, now only 2 female guppies and 7 fry, 2 leopard danios.