Lots of variables in growth rate, food amount & frequency, water changes, internal parasite load, dominance in the group pecking order. IME they grow fairly fast from 2 to 4 inches, moderately to 6 inches then much more slowly. The largest I've ever grown were ~7+ (SL, + tail ) inches after maybe 8 years starting with 1.5 inch clowns but some were a bit smaller.