My last betta used to build the biggest bubble nest when the water was cloudy and three days old, people would think its dtergent suds in there, so I wonder if they like dirty water.
Nope Nope Nope. Bubble-nesting is an instinct that has nothing to do with the 'happiness' of the betta. But when your water is fresh and clean, and/or the surface of the water is agitated by a filter, etc. the bubbles break apart and pop faster. If your tank has stagnant, dirty, filmy water the bubbles will last for much longer because they are thicker (ar gross as that sounds

).