Actually, I was thinking something similar the other day. I use AquaPlus, which has EDTA as far as I know. I was also wondering if that may decrease the availability of iron. But, I have flourite, so I don't think it would be a problem even if iron was chelated from the water column. Hopefully it's not picking up anything out of my Tropica Master Grow. Now I'm thinking I might switch to something else just to be on the safe side....
I really doubt that the amount of heavy metals in tap water would harm plants. Unless you have bad pipes or some other water source that may be high in metals. I wouldn't worry about removing heavy metals with water conditioners.
As for the aloe, I don't see the point. That's my personal opinion, and I don't have a basis for it, I just think it's useless. I've used Big Al's conditioner though, and that has aloe. I can't say that my plants died or anything, but that was right when I set up my tank, so I had plenty of problems as it was. I've never heard of anyone having problems with them though.
