I can tell you, it depends on the fish, my six line was the first fish on my tank ( I got it for flat worm control) and now I have 14 fishes, and all she has killed was another six line i added, actually, the original six line, jumped out, so this is about fish number #8...
I have 6 Chromis, 3 false peculas, 1 sailfin tang, 1 cleaner wrasse, 1 blue hippo tang, 1 royal gramma & 1 six line, i always get a six line about $10-15 depending adn they always do good on my tanks