How big will your plecos grow in a 6 gallon tank?

Plecostomas grows anywhere from about eight inches to three feet. So anything less than 50 gallons would be, to put it frankly, laughable. Any smaller and the fish would die from stunted growth LONG before it's time. Stunted growth in fish is when the body stops growing but the organs continue to. Eventually the fish dies after months of slow, progressive agony.... It ain't worth it.