I will be soon getting a 300 gallon stock tank that will be housing 13 turtles and a large pacu. I know they are all very messy so I was wondering what would be the best method of filtration.
I'd do a radial flow settling tank followed by a mechanical filter with socks or floss fed by a solids lifting overflow (SLO) for the overflow. A fluidized media would be easier to keep clean for bio. You can score used 55 gallon drums from beverage industry or online for super cheap. I picked up several for $15 each for a future project.
Sounds like a lot of bio will be needed... whatever way you go, make sure to add lots of potho (house plants) on top of the tank.
I hope the tank is glass btw, turtles and acrylic usually end up with an upset owner from the scratch marks