Bubbles coming from heater

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a.k.a. achu
Dec 1, 1999
Austin, TX
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Anyone else notice this in their tanks?

The 50W Tronic heater in my 15 gallon tank occasionally sends up a bubble of air, maybe about once an hour. As far as I can tell, the heater is still working correctly, there is no water in the heater, and the glass tube is not cracked. Anyone knows what's going on?


Cardinal Rule
Feb 22, 2003
Pacific Northwest
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Small bubbles often develop on the heater while - or after - it's been running for awhile. This is normal. Hot water holds less gas than cool water. The water immediately around the heater while/after running is warmer than the water in the rest of the aquarium; thus the gases that were dissolved in the water when it was cool are being driven out. You can see this phenomenon when running hot water from the tap - it begins flowing cool and clear and as it gets hotter it gets more cloudy. The cloudiness is many tiny air bubbles being released from the water as it becomes hotter.

If this is what's happening, you should see lots of tiny bubbles on your heater. As the heater continues to run, more and more bubbles will appear. These will stick together to make slightly larger bubbles and eventually rise to the surface.

To be on the safe side, examine your heater carefully for signs of leakage: water or condensation inside the heater; severely discolored ceramic and/or cotton inside the heater; or black marks on the inside of the heater glass. If you see this last thing, the heater is shorting out and should be disconnected from the power supply immediately.