Just an FYI, 99% of the dechlorinators we use are "not approved for use with fish for human consumption". I do not know why, but would suspect that it would apply to the plants grown in it too.
Blame the lawyers. (Yeah, and I'm married to one.
The standard ingredient in dechlorinators, sodium thiosulfate, is pretty safe. If I'm reading things correctly, it's not recognized as hazardous.
I'd worry more about bacteria from the tank than the dechlorinator.