My six month old 75 gallon tank has BIG problems with ammonia level at 8.0 ppm, nitrites at 0.50 ppm and nitrate at 20 ppm. I have cleaned my filter, did a 50% water change, added Ammo Lock, Stability., and Stress Coat. I am at a loss of what to do next. We’re losing 3-5 fish a day for the...