The set-up - Which I should have started this blog with.

Pictures detailing this will follow, at which point I will delete this little bit of text.

The Pacu are currently living in an 75 US gallon tank - 48"x18"x20" high.  It is filtered by a sump tank (about  14 US gallons) with lava rock and plants (with a 24" T5HO light on it), as well as an AC 70 HOB filter, with just sponges.  The sponges on the HOB are just to pull particulates out of the water column, as that was a pretty big problem right from the start.

There is an automatic feeder set on the AC 70, that pours food into the outflow 3 times a day, 6 hours apart.

the lighting on this tank is a 48" T5 HO (May not be HO) corallife fixture.  I would recommend against them if you have contact between the bottom of the fixture and the top of the tank, fyi.The plastic "shield" for the bulbs melts a bit.  There is a 24" 2 bulb t5 HO on the sump, to help the plants that are in there to grow. 
In the sump is lava rock, and a few bioballs, as well as Anubias, Hygrophila, and some java fern, perhaps.


There's a bunch of slate in the tank, to make spaces for the pacu to feel comfortable.

Pool filter sand substrate, and there may or may not be any Malaysian trumpet snails left in the tank.