jealous and aggressive dog

[billxx]

really need some help or advice on this one, I have 2 dogs, shih tzu (female 2y.o) and a poodle (female 2y.o) they are only a day apart in age, and I adopted them when they were almost 4 months old, but i adopted the shih tzu first, then after a month i adopted the poodle. we noticed that the poodle always fought the shih tzu, their first super aggressive fight was when they were about to turn 1, we thought at first that it was normal, since they said that if u keep 2 females there would be times that they will fight. as time goes by the jealousy and aggression towards the shih tzu got worse, they wouldn bite each other till they bleed, we used to punish the poodle by locking her up, but now whenever they fight we just turn all the lights off the room and they would stop, weirdly they don't fight over food and even share and exchange food when they eat. then we tried shifting our attention more to the poodle, the shih tzu didn't get aggressive over her, but nothing changed the poodle still fights the shih tzu. Whenever the poodle would see us or have a glimpse of me playing with the shih tzu she would run towards us and tower over the shih tzu, the shih tzu would then go tense. the poodle also fights the shih tzu when she gets shocked from loud noises. right now we don't really know how we can put a stop to these fightings and aggressive behavior of the poodle.