I currently have a 75 gallon tank with a clown knife, a pleco, green scat, silver scat, and a pacu. I was hoping to put some aquarium salt in my tank but im not sure how much or how quickly.
Your scats are BW fish. The others are actually the opposite--softwater fish. The clown knife & pacu will grow to 4 feet & will outgrow that tank. I'd find a new home for them (knife, pacu & pleco) & get another scat, as they will grow as large as your outstreched hand & are heavy waste producers.
Also aquarium salt won't cut it for brackish water. You need marine salt, same stuff used in saltwater tanks. And you will need to knwo what specific gravity you want first and get a hydrometer.
And yes, you will need to find a new home for the freshwater fish.
I was told by my LFS that i could keep my pacu and scats together for awhile until they got bigger. i was also under the impression that the red bellied pacu would barely get bigger than a foot. i am actually planning on buying a bigger tank as soon as i get the money but that might take a year or so, but right now all of my fish are under 3 inches and i was told that as juveniles the scats could be kept in freshwater or low salinity brackish water. I also plan on getting rid of the clown knife eventually.
Why are you buying fish you can't keep for life? How can you be sure you can place a giant fish in a home that can house it properly? Please don't listen to folks just trying to take your money & do some research on the fish you're interested in, before you purchase them.
I have been doing a lot of research on the fish i want. I did research for about a month before ever even getting the tank and i mostly read that the scats can be kept in freshwater, brackish, or marine. I mostly go to http://www.**************** and http://www.liveaquaria.com to research.