we have 30 in a 55gal, 60 in a 125, 150 in a 75 (1-3in. growout), 50 in another 75, and a few 35gals with 50-60 fry in each. the 35s have air filters but the the bigger tanks all have a minimum of 2 emperor 400s on each. fx5 and emperor 400 on the 125. we like to keep our tanks overstocked to reduce aggression and make good use of space. it does take a bit of finness to keep the tanks peacefull and get the right mix for each tank. just make sure to keep up with water changes and watch for excessive aggression.