Something strange happened to my heater... Any ideas?

[Penny]

I woke up this morning to find a patch of bubbles in one of my tanks.. I tested the water and everything was perfect so I scooped out the bubbles and kept and eye on it.

Then I noticed the bottom cap had come off the heater. (It's a little 25w glass cheap one, but its adjustable and seemed to be doing the job)  I popped the cap back on. Then I noticed the the heater had bubbles all over the under side and it was making a steady stream of tiny bubbles (exactly the same size and consistency as pearling) 

Turned it off and let it cool in case it was over heating (water felt normal and I didn't get electrocuted) when I removed it the heater I thought I'd find it cracked but it had this weird stuff on it.. only in a patch and only on the underside. It's hard and crunchy like pumice stone. There's no water inside the glass

The heater has only been in the water for about 7 weeks.

🤔 Any idea what's up with it?

Thank you 😊

[JettsPapa]

I don't know exactly what happened, but I'd be very hesitant to put it back in the tank.

[Streetwise]

Looks familiar to me! This is a failed heater, probably cracked.

Edited December 8, 2020 by Streetwise

[Lee626]

It looks like scale formation like what you’d find on the heating element of a kettle, as if the water had been boiling locally around the glass.. but an aquarium heater shouldn’t get anywhere close to hot enough for that to happen... very odd 🤔

[RockMongler]

It could have just been a small leak of current out of the heater.  You can do electrolysis of water (breaking it into hyrogen and oxygen gas) easily with just a 9V battery.  Over a few weeks, that could give you a build up of stuff from the water, and give you an effect similar to pearling.  Might not be enough to give you a 'shock', but enough to break down the water into its constituent elements, and probably do some scaling with the other ions floating around in the water.

I would probably not use that heater anymore.