Using other makes of ceramic rings is fine and filter wool the main media are the black Rena filter sponges which you have so wouldn't think the media is at fault, you didn't say how often you clean the filter, I clean mine roughly monthly and it is fine with that, a few more questions
do you have any water readings, as for the green murky colour sounds like algae, how long do you have the lights on for and do you have any live plants not easy with goldfish I know