You have been receiving some pretty good advice here so far. Just to make sure everything is summed up:
1) Your Pacu will get HUGE. They can grow just under a yard long and can live for up to 20+ years. This growth will take a while (they slow down as they get older), but this is something need considering. Whether it be to put them in a pond, or give them to someone else when the time comes you still need to think about it.
2) You kinda have the water change/filter cleaning regiment backwards. Fish put out the majority of their "waste" as pure liquid ammonia. That poop you see coming out isn't the half of it (literally). Thankfully there are free-forming bacteria colonies present in any body of water that has ammonia present that will process this to a much safer. Did I mention that ammonia will kill fish in hours, not days? The bacteria likes low light and high O2 content, so the filter media is one of the best places for them to grow. When you take them out/wash them in chlorinated water... you are starting from square 1. I would say as soon as you can do a HUGE water change. It's not the best idea, but it sure is better than leaving them in ammonia.
3) Aquarium salt is the exact same thing as sea salt, kosher salt, pickling salt, or canning salt. Any non-iodized salt will work. 1 tbs/10 gallons of water makes a great stress tonic to help fight off disease and such.
4) The next best thing you can do is bump up your temperature. This could be a problem for the goldfish though. You are missing a potential life saver by not being able to do this.
When we say your tank is overstocked and needs upgrading, it isn't because we are trying to be critical. It's because you obviously give a crap by even signing up for this site (doing better than most already!) and we want to see you not waste any money/innocent fish lives. This is a great community that is better than than the rest. You came to the right place!
P.S. While they like veggies, they LOVE fruits.
P.S.S. It would be helpful knowing what kind of filtration you have running.