A pacu in a 180? Seriously?
You need to reconsider the way you care for your animals. Its not really fair to them to force such big fish into such small tanks.
That cat fish needed a tank more than 3x the size it is in a long time ago. Please for the sake of the animals that you took on the responsibility of caring for, get either new and proper homes for the fish, or get tanks that are appropriately sized. A 450 would take care of everyone but the cat fish for life and the cat fish would be in good shape for at least the next 6 months.
When you say 50% biweekly, do you mean 2x a week or every 2 weeks. Your water is green, that says you don't change even a fraction of the water you need to. With that bio load, you would need to change 50% of your water a day and I am not sure even that would be enough.
I am afraid to ask..... how big is the pacu and how long have you had it?