I'm glad you're a responsible fishkeeper. I agree with the others--400 gallons is too small to properly house pacu for life. Pacus can live 30+ years in a good environment. That's a very long commitment to a fish. If a person is going to "do the right thing", they will find it very difficult to find their beloved pacu another home when they can no longer take care of it. Silver dollars would probably be perfect for you if you want the pacu look.
To thrive, pacu need good water parameters, i.e., nitrates 20 ppm or less. With poor water conditions, pacu live about 2 years. The bigger the fish, the harder it is to maintain excellent parameters in a small tank. It is possible, but it is not easy. It can also be very difficult to upgrade to a bigger system. We have been trying to upgrade for over 3 years.
Here are our poor pacu in their pathetically small 300 gallon tank. They don't have much water to swim in.
We are in year three building an addition to house their new tank. An impulsive, spur of the moment yard sale purchase (a 55 gallon tank with two pacu, four oscars and two pleco) has resulted in a life altering, very very expensive experience.
