I agree with the others, with that stock (even with juvie fish), you should be doing "at minimum" 40% water changes per day.
Then you will get growth, but then the problem becomes, that only the oscar is fit for a 150 gal tank.
In nature Pacu are primarily vegetarian, so Tilapia (although reasonable for the other fish), is not that great for the Pacu.
A friend has 3 adult Pacu in a 10,000 gal tank that are about the size of garbage can covers, with some oscars and 4 ft red tail cats, and feeds the Pacu separately with bananas, other fruit, and vegetation type foods.
The pacu and cats as adults will need at least 1,000-2000 gallon tanks, and will still need daily water changes.