I need help. My 30 gal. is having trouble with fish dieing.It's not a new tank, it has been up for 2+ years. Recently my fish have been dieing slowly.I had three grourami's(1 golden,1blue,1fire),1 albino corydora,and 3 glow lite tetras. The aquarium water is crystal clear, nothing funky about the tank. The filters are running, the temp is fine, I even have a bouble wand across the back. The only thing I see that is odd is that the air hose has a white film on it, and none of my other tanks have that. I have not yet tested the water. Any ideas are appreciated.