[ToddHotchkiss]

I made a fountain out of 6" square aluminum tubes. I'm pumping water through aluminum pipes to about 12" from the top of these square tubes. The water overflows, creating a pleasant sound, as it spills over the edge. Lately, I've noticed that the water is fizzy, and off-gassing. There must be something going on chemically. Any ideas what it could be?

[Borek]

The only thing that comes to mind is that aluminum tubes - if in water and in contact with other metals - will easily undergo galvanic corrosion.

Doesn't have to be the culprit here, just a first idea.

[Corribus]

Before invoking chemistry, are you sure you're not just drawing air into your water line?

[ToddHotchkiss]

BINGO. I added water to the underground reservoir and the fizziness disappeared. Thanks!