Copper was and honestly still is one of my main concerns-once its there its there. Also I read that Seawater levels of copper are like 10-40 PPBillion and if that is true, then having just 40 PPMillion is a whole lot copper. On the other side of that argument-I would think that the Magnesium in the water would have some sort of binding effect on the copper to the point that some would not be taken up by the corals and accumulated-I could be very wrong on this though

Actually it is not nitrates or ammonia or phoaphates that are the problem for the more delicate corals. After all macros and other algae can consume those from the tap water and the much higher amount from the bioload from the fish.

the real problem is copper, strontium, and other ions. Those do come from the water with less contribution from the bioload.

So if you use macro algae to keep those things at bay and limit the effects of the tap water by just topping off, you can maintain successful reef tanks. But you do have to provide the light and food the corals need as well.

my .02

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fw leiden since 1979, fo salt since 1979, mixed reef 55g 2002-2009. Strong emphasis on the tank taking care of itself. Balanced with plant life, no water changes, tap water, no filters in FW. Only dosing calcium, alk, mag in marine reef tanks. http://www.aquariumforum.com/f15/my-...ods-26410.html
recent tanks (till 2009) 7 years- 10g FW leiden 7 yrs, 55g mixed reef 7, 2 yrs, 20g FW leiden, 10 g fw leiden , 29g mixed reef, current tank 55g leiden