Question
We have a fairly large pond with a river going down a hill.  We have a large headbox (approx 5'x3'x4') with filter material and lava rocks.  I started the pond for the year over the weekend and everything was fine.  But the next day small to medium sized bubbles are gently floating to the surface of the headbox from under the lava rocks somewhere.  I had this problem last summer as well.  It seems to slow the water flow slightly, but not much.  I'm just really confused on how air could be getting into the system.  The pump is fully underwater and not sucking any air.  Where else could this possibly be coming from??

Answer
Hey Dan I am not sure. I take it you cleaned the filter box, sometimes new material will cause bubbles as new water does. It could be the water is churning in the filter box causing air bubbles. They sound like they are coming from the filter box and not the pump. Check your lava rocks.Are they still porous. Thanks Eirc