If it really seems like air, it'll cure itself with us and movement. I wouldn't worry.
But, just to double check, any chance there is residue from the tank cleaning, e.g. cleaner?
Is your pump coming on often without a reason?
Do you see water dripping or accumulating or wetness anywhere?
Do your bilge pumps run more often?
Is there any odor to the water?
Is the water heater tied to the engine? If so, any change in the engine's coolant level or specific gravity?