Bubble nests are one of the few traits that makes Anabantoidei fish so interesting and unique. The usual formation of bubble nests in tanks show signs of breeding behaviour, good health, as well as happiness. However, although bubble nests are seen as a good sign, they can also act as warning signs for a fish or ill-health.
A healthy betta: Bubble nests should be well knitted together, made of small to medium sized bubbles (bubbles generally no bigger than the mouth), and should be quite strong and not easily pop when reaching the surface. Bubbles should not seperate by themselves easily, and should be well compacted.
A sick betta: A sick betta blowing bubbles often blows medium to large mucousy bubbles around the surface, but not in a group. They will be randomly blown and all around the surfce of the tank. These bubbles are caused from surface dwelling and exhaling oxygen that is taken in from the labyrinth.
Although this may seem odd, bettas and other anabanotiodei species can easily blow few bubbles and form a displaced bubble nest, or even just randomly blow large bubbles. Bettas who are ill and blowing bubbles will generally act sick, showing clamped fins, rapid breathing, stress lines, lack of eating, colour change, and bottom sitting.
There is no need to freak out seeing these sorts of bubbles, however they are a great indication of when your betta may be a little under the weather. A betta that is swimming and acting normally excluding a few displaced, large bubbles is nothing to worry about.