My situation is that my fish are getting sick suddenly. The tank is a 55Gal that has been active for about 2-3 yrs. now. It's been moved twice about 1 year ago. And has been flourishing since with 6 Cory Cats, 1 Tiger Barb, 2 CAE, 1 Otto, 2 Cherry Barbs, 1 Bala Shark, 1 SAE, 1 Lemon Tetra... I...