Need Help to Eliminate Bubbles from Overhead Filters

[H]-[H]

As per title, I've been having trouble with both my overhead filters creating bubbles from the return pipe..
It was originally a single pvc pipe but I added a 90 degree pvc elbow thinking it would reduce/rid the bubbles but the problem still remain..
The bubbles bursting is making my floor wet and not to mention it's not aesthetically pleasing..
Any ideas on how to get rid of the bubbles?
Thanks in advance.

 

[deeda]

Try placing a piece of aquarium safe foam in front of the return pipe to the aquarium. It may help to break up any air bubbles.

Is the return end in the aquarium above or below the water surface?

 

[H]-[H]

I went and added a few more elbow joints to the existing return pipe so the water flow upwards instead of straight down.. It was still creating bubbles when water flows out hitting the surface..
Then I found a sponge lying around which was originally from a return pump.. Needless to say after adding the sponge, no more bubbles.. not even a tiny one..

Problem now is I need another sponge like this for the other overhead filter return pipe..
I have a few sponges that I can cut out to size but how to make the perfect center hole in the sponge?
Size of the hole is 20mm if that matters..

 

[deeda]

You can cut an X into the sponge using a sharp knife and just slide it over the pipe opening. No need to cut a circle to fit the pipe.