Rack system gargling

[cane]

Just finished my 8 tank breeding rack and everything is working well except every once in a while the system seems to burb and gargle sending a rush of bubbles and water into the tanks scaring the fish. The tanks are all plumbed together to one drain and one fill pipe. Would drilling a hole at the elbow of the drain pipe and inserting a tube help or cause a problem. Any recommendations would be great.

Pics are to show how my system is set up.

 

[TheEngineer]

The big bubble comes from the return or the drain?

 

[cane]

Return

 

[TheEngineer]

Best guess is that the return pump is pulling in air and it is accumulating in the plumbing until there’s enough for the bubble to make its way out.

Is there any air getting into the return pump? Even microbubbles.

 

[cane]

I do have a lot of micro bubble going in from the drain. I’ll put a filter sock on that and see if that works.