Reddit mentions of Two 1" Inch Stainless Steel Bearing Balls G25

I've settled on these

https://www.amazon.com/gp/product/B007B2A84S/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

1 inch stainless steel balls, they are surprisingly heavy for how small they are, which is great because I can add as many as I need to counteract floating without being bulky

one on either side of a bag will weigh down even the most air filled bag

That's why I suggested clear marbles, to minimize the impurities, but clear leaded glass crystal is a thing. OP could also pick up some large food grade stainless steel or ceramic ball bearings, but I didn't suggest that originally because of the expense.

https://www.amazon.com/Inch-Stainless-Steel-Bearing-Balls/dp/B007B2A84S

https://www.google.com/search?q="food+grade"+large+"stainless"+steel+ceramic+"loose"+"ball"+bearing

But ultimately you could play the "possible unsafe impurities" game with just about any material unless you personally have it tested.

A friend of mine uses a large stainless ball bearings as whiskey stones.

I use these