so in my 58 gallon i have lemon tetras black neons and gymnogeophagus growouts. i have two ac110 filtering water qaulity is 0 ammonia 0 nitrite and 10 ppm nitrate. i do weekly 10 to 25% water changes. over the last month and a half of being cycled and running ive lost three off my lemon tetras mysteriously are they just a week strain of fish am i doing something wrong