im not arguing that, as iam a fool on this particular subject, but i dont really beleive it is likely they will eat eachother, the FBT live aboe the water line, and the DAF below, the later are really to small to be a threat to the former, and the former is unlikely to forage on the bottom for food and find one of the latter.
even so, on top of toxins, diseases are also a threat.
i mix these, doesn't mean you should.}