hi I have a 75g. that i cycled for 3 weeks before I added a clean up crew of hermit crabs and 5 turbo snails. Now everything was fine for 1 month with this crew, also added a fourline wrasse a coral beauty and a purple lobster, But in the last few days 4 turbos died. did a water sample, came out perfect. The only thing chemicalwise that i added was phosban 2 weeks ago because of hair algae and now the tank is crystal clear with just coraline algae showing on the live rock. any explanations would be app. thanks