What fizzes when dropped in a clear glass of water like alka seltzer but lasts longer -an hour or more.?

I need to create bubbles in a glass of water for 1-7 hours. The container holds as much water as a juice glass.


Thank you.


(intelligent answers pls - forget the sarcasm, thx)What fizzes when dropped in a clear glass of water like alka seltzer but lasts longer -an hour or more.?
perhaps dry ice. (solid CO2)