Jardin Muffler Air Stone Connector 2-Piece Brass Underwater Air Stones for Aquarium

I would not use these in a salt water setup as a matter of caution even though the supplier says it's safe for both fresh and salt water tanks. I doubt much copper would be leached, but with $100 or better per fish it would be rolling the dice, and they are pets as well. I use two in my 36 gallon fresh water with no issues and so far no sign of oxides or corrosion.