Unless there is some kind of loophole where phosphate free doesn't necessarily mean 100% phosphate free, I think Marineland is legally bound to provide to the consumer phosphate free carbon, as they claim their Black Diamond carbon is. This is indicated in the small pamphlet they put inside the jar, on top of the carbon.
To me, Johnny Consumer, phosphate free means no phosphates. Period.
It'd be a good one for that TV show "Marketplace". They could test the stuff to see if what they say is true. But then, most people that watch the show probably wouldn't care.
Cheers
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