Bubbles in a 3 gallon eclipse?

[papa_bear_21]

We have a 3 gallon eclipse, used primarily as a fry/breeding tank. Currently it is home to our 2 female platies, and a otto cat. I've been seeing a lot of whit bubbles forming around the filter return, and it has my interest. I have not done a recent water test, but at the last test, all perameters were in check, ammonia 0, nitrites 0, nitrates 0, ph 7.9. The bubbles do not spread over the top of the tank, and they do not look like soap bubbles. The fish seem happy, and normal, but this is the only tank this exists in. What could be the cause of this, any ideas?

 

[theotheragentm]

It could possibly be a film from oils from food. Take a paper towel to the surface of the water to clear up some of the film on top.