How big do koi grow in a 1500 gallon pond?

Koi can grow quite large, especially in a well-maintained 1500-gallon pond. Depending on the pond's size, water quality, and diet, koi can grow up to 36 inches long and weigh over 18 pounds. However, most koi will stay much smaller, with an average size of around 12-18 inches. To ensure your koi reach their full potential, regularly test your water quality and provide them with a diet specifically formulated for koi.