Puting red devil in aquriam

Question
i have 30g fish tank in tank i have 4 oscar,4 pacu,1 arwona. Can i put a small red devil in tank?

Answer
Karen,
No you should not add the fish and here is why. One Oscar needs a minimum of 75 gallons all by itself. Two Oscars need a minimum of 150 gallons. You have four so your tank minimum just for them is 300 gallons. Your Pacu can grow to 36". So you are looking at a very very large tank. Most will tell you 500 gallons per Pacu, you have 4 so they will need a minimum tank size of 2000 gallons. The Arowana needs a tank no smaller than 200 gallons. So, in order for you to house the 9 fish that you have, the minimum tank size is 2500 gallons. The fish you have have are monster size and need a monster size home. They most likely already out grew the 30 gallon tank. I would suggest getting a much larger tank, or think about rehousing the ones you have.