Do ziplock bags break down in tank water?

[justinl]

flexible plastics do release some nasty chemicals into water, even more in saltwater and even more in warm saltwater. That said, unless you never do water changes and your sump is full of the things, the amount released will be negligible. they will not decompose any faster than the silicone your tank is stuck together with; estimates range from 20-1000 years. I still wouldn't leave them in there indefinitely

im also curious. what are you using them for?