I use sea fans in my 150 gal tank and never have had a problem. The snails might have been the cause. Suggest you clean ypur tank with hot salty water to kill and snail eggs, snails or funguses. In the future to control snails I would suggest you look into clown loaches (min 3 ) or golden dojo loaches. They love snails and snail eggs. Use them in all my tanks.