Cobalt glass has cobalt in it (that’s what makes it blue). Whether any of the cobalt is able to react with the saltwater or whether it is totally inert I don’t know.
If it were me, I would a either put a small aragonite rock in there, find clear marbles or just use 200 micron filter socks and not worry about it. (I personally use 200 micron mesh socks).
If it were me, I would a either put a small aragonite rock in there, find clear marbles or just use 200 micron filter socks and not worry about it. (I personally use 200 micron mesh socks).