Thanks everyone for your thoughts.
As for the cainster filter in a fish only tank: it's not ideal, but completely doable you just require plenty of dilution. A pair of clowns and firefish in a 90 gallon with a Fluval 405, is more stable than a 30 gallon with 30lbs of liverock. But in a stocked tank with larger fish lr and a lot of flow is better.
I recently restarted the tank and picked up some more fish. My lfs, gave me 50% off, but were of no help as to the sudden death of fish.