I just finished with the WC in the diatom tank, refilled, turned everything back on and heard a noise that sounded like air being sucked into a filter. I unplugged all the filters, and could still hear it. Thought it was the PH for the co2, unplugged that and still heard it. Then the glass tube blew off the heater. Thankfully it blew downward, instead of exploding. This is the first time I have ever had a heater do this. The glass tube is just friction fit over a rubber barb type fitting. The noise was the heater boiling the water that got inside the heater. WOW!!