We currently have 12 fish in the 120 gallon (most of the fish stay small). I used to keep a much heavier fish load but I learned my lesson. When the tank was overstocked my nitrates would be between 10 and 20 ppm even if I did a 25% water change every 2 weeks. Since lowering the bioload my nitrates are less than 5ppm now with only a monthly 25% water change. It is much better to enjoy an easier to maintain and healthier tank than to have more fish to look at.