Stopping the bubbles?

csmaster

AC Members
Oct 26, 2001
51
0
0
Derbyshire, UK
My tank has an internal filter which is fully submerged, but every few minutes it will spew out a bunch of small bubbles, I dont think there is any air traped in it as its been doing it for about 2 weeks, the only thing I can think of is the bubbles off the plants are getting sucked in, but there arent that many bubbles. does anyone know how to stop these bubbles?
 
I'm assuming there is a sponge prefilter on this? If so, when you remove it from the water for cleaning it could be trapping a good amount of air in it. Can you see alot of bubbles on it? Maybe you just have some algae growth on there producing tiny bubbles that accumulate over time?
 
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