I purchased a 240 gallon (8x2x2) aquarium with the intentions of owning a black arowana. I made a 50 gallon sump filter courtesy of youtube (uarujoey's upload). How many times does the water have to turnover since they originate from the calm waters of the Negro river basin? I've read somewhere within the 5 times realm would be sufficient but not sure. I dont plan on heavily stocking the tank, possibly a 3 larger predatory fish (havent decided on tankmates). thanks again