the dreaded worms

[Delphinus]

Go with a canary wrasse (sometimes called yellow coris wrasse - although it's not a Coris genus at all - nowhere near as big). Gorgeous fish, bright yellow, and will decimate any flatworm population you may have. Look up "Halichoeres chrysus."

Not sure if I'd keep one with a sixline though. Sixlines can turn mean and aggressive as they get older - and are more than capable of inflicting a lot of damage on their perceived enemies.