Ok.. I hate to complain about the size of someone's tank . I think a lot of us on MFK have fish that shouldn't be in our tanks. You can extend that argument that fish shouldn't be kept in tanks and should be left outside.. not captured and flown in bags to the store and then sold to us for our enjoyment... but there is a point where it goes beyond keeping something as a pet that might be better left in the wild because it's not domesticated, and cruelty to animals.
My suggestion is to euthanize or rehome every pacu. They can be given to people with bigger tanks or you could build something huge for them. Tough lesson to learn but has to be done. I think you will be hard pressed to rehome that many monsters, and i doubt anyone here has the finances to care for 9 pacu.
40gal tank with 9 smaller size Red Belly Pacu,a Cichlid, and a Pleco.
Euthanasia or re homing as stated above. Or build a several thousand gallon enclosure for them. I have a 350g coming that's going to hold the two i own, and that's probably a little cruel, but at least they don't have to live in a 40g, right?
26gal tank with 5 Neon tetras, a Black Tetra, 4 Tiger Barbs, 2 Opaline Gourmi, a Dwarf Danio, and a Rainbow Shark.
I don't think the tiger barbs should be with other fish. I'd rehome them and the dwarf danio (or get him some school mates). Move the rainbow shark to the 40 gallon once the pacu are gone.
10gal tank with 20+ Guppies and what we think is a Pluppy??
Reduce the number of guppies, give the females away to kids or petstore or something. Keep the males.
8 gal. tank with 3 Mollies and 3 Neon Tetras.
Move the neon tetras to the 26 gallon tank with the other neons. Rehome the mollies or purchase a larger tank like a 20 long for them they belong in their own brackish water tank.