Most eggcrate is made of thermoplastic. It doesn't have any phosphates directly in it if it's polystyrene (which the white eggcrate usually is pure polystyrene). Make sure you wash it really really good to get any residue off that may have been left on during manufacturing. There was an article I read once on some forum (NY Reefers? Maybe NJ?) that some guys in a chemical engineering lab actually tested the stuff and they couldn't force it to leach phosphates unless it came in direct contact with a kalk solution, and even then you're talking minute traces ( something like 0.01% by volume or some nonsense leeching out over the first 40 days).