DO NOT PUT THEM IN THE TANK!
casings are made from brass and it is poisonous when ingested.
thats why cavalry regiments were silver instead of brass, ended up killing the horses when they had the brass fittings in there mouth so they changed to brass.
long story short but yeah don't put them in, from what i have seen they will start to oxidize within few days of exposure, cant say how long you will have underwater.
not worth the risk!