30 fish in a 150? Sounds like stress induced ICH.
The only way I know to kick ICH is to get ALL the fish into a tank where you can do a 6 - 8 week hypsalinity treatment while leaving the main tank fallow.
That's going to be tough in your case. You may need to go the opposite way and remove all inverts and coral to another system while you bring the main tank down to 1.009 SG
for 4 weeks.
Hence the question: What else is in the tank?