Bubbles in Dwarf Puffer Tank?

you do realize you are seriously overstocked ... an 8 gallon tank is not even big enough for two dwarf puffers ... it is 5 gallons per dwarf puffer and while young they may seem all friendly and cute, but when they mature, your tanks is way too small and there will be fighting and possibly death ... i have had dwarf puffers for almost ten years and i have never had any bubbles show up at the top ... i do not believe it is a nest as my puffers spawned and there were no nests at all ... they lay eggs and mostly eat them if not removed ... what are your water paramaters ??? is ammonia 0 ??? nitrites 0 ??? nitrates less than 10 ??? i would assume you are having issues because of being overstocked ...