My biggest problem with this theory is that even if the macros *do* uptake bad things, there is *nothing* that will keep these same things (copper, heavy metals, crud, etc) from being absorbed into your corals.
Just because the macros may pull some amount out of the water column, it's incorrect to think your other denizens won't be affected.
You don't need to worry about your corals absorbing what isn't there to be absorbed in the first place...
The other issue is you need to still export your macros. I have no idea, but isn't there some kind of limit on what they'll uptake? I find it hard to believe they'll continuously suck these items up. Of course, it could be that the level at which the macros would be 'full' is way beyond what we would see in a reef tank, so this could be a moot point....
Just another .02
Just because the macros may pull some amount out of the water column, it's incorrect to think your other denizens won't be affected.
You don't need to worry about your corals absorbing what isn't there to be absorbed in the first place...
The other issue is you need to still export your macros. I have no idea, but isn't there some kind of limit on what they'll uptake? I find it hard to believe they'll continuously suck these items up. Of course, it could be that the level at which the macros would be 'full' is way beyond what we would see in a reef tank, so this could be a moot point....
Just another .02