hi sue... we use to have a huge salt water fish tank, loved having it too... we had a couple very large handmade ribbon cores that had cerainly seen better days, so we put them in the tank. they looked gorgeous! when I would clean the tank, I'd just sorta wipe them off under water, never took them out. after 8 years a well meaning person bought me a fish, it had something nasty that killed my entire tank (sniff!) talk about seeing hundred dollar bills floating... ewww.
anyway we took the marbles out not thinking much about them at the time and put them in the kitchen window for sun catchers. noticed about a week later they had shattered, but from the inside out. kinda like a car window breaks in those little weird shaped pieces? only they were still whole. it was amazing. the only thing we could contribute it to was the years in the synthetic salt.