A little extra bit of info I've picked up: Food-grade or potable doesn't necessarily mean "safe for reef life" (and some would argue that it doesn't mean "safe for humans" either...). Honestly, I don't know the details about the controversy but like Marc said, HDPE is a safe bet. It's very stingy with it's molecules, so to speak.
On this topic, I'd consider the source. Eric B's worst guess is probably better than my best guess ;-)