If your 320g is setup and filtrated and running why aren’t the ray and jardini moved over?... Why are you housing pacu? Go return them to whoever sold them to you before you wind up being one of those people on marketplace trying to get rid of their pacu that’s overstocked and in poor health.
You have 550$ to spend on a tank but don’t have 120$ for a solid mag drive pump and 30$ for the materials to put together a solid drawer design w/d tote sump? If you aren’t even willing to spend 70-170$ on filtration why are you trying to keep motoro rays and jardini arowanas and all these expensive large fish and set up a 320g tank? You do realize 320g tanks aren’t cheap right? 70-170$ is chump change when it comes to setting up such a large tank.
I’d love to know what you think “normal” and “perfect” is for your water conditions. I haven't seen an actual ppm reading results posted in this entire thread on your water's actual perimeters. I seriously doubt w/ bi weekly wc your water conditions are in a healthy range. Why do you keep saying “water chemicals are normal?” Btw 50% wc a week isn’t really that much. A more realistic wc would be 70-80% weekly for fish that produce a heavy bioload and from my understanding rays do produce heavy bioloads.
You would know if your water was getting worse or even in healthy conditions if you know how to read a chemical test kit and were remotely knowledgeable about the nitrogen cycle that takes place in your aquarium. You don’t seem to know the first thing about keeping these non novice fish, or how the nitrogen cycle works (or even possibly what it is) and water perimeters.
Seriously, do yourself and the fish a favor and return them all and do some research on fishkeeping, read an article on the nitrogen cycle, what it is and how it works in your aquarium, start with something more beginner, and LEARN before you jump into something head first without knowing anything about it. This isn’t meant to be harsh but after reading this whole thread and a few of your others this is ridiculous…