the tank with growth limited by nutrients and copper levels you report, I assume that this is also the tank that you are adding iron to?
Yes.
When you began adding iron, do you know if the copper levels dropped? When you add additional iron now, is there a further reduction in copper levels, with or without associated macroalgae growth?
I have not measured copper until recently, so I don't know what it previously was. I add iron once or twice per week, so I wouldn't expect copper fluctuations (or maybe not even macroaglae growth fluctuations) on that time scale, but I've never tried to measure it.
Also, I am wondering what element is limiting here-presumably phosphorus? I wonder what additions of phosphorus would do to copper,
I don't know. It might be nitrogen, phosphorus, or maybe even a non nutrient like space, light, etc.
That's an iunteresting concept: adding pure nutrient chemicals to spur algae growth that in turn take down metals levels. Of all the suggestions that I've heard, that might be among the most likely to be useful, inexpensive, and with little in the way of potential side effects.
Can you recommend a procedure for getting some samples tested- perhaps an initial testing of copper levels in a limited number of Eco-Wheel tanks? And the approximate cost per test, if you know? I'm interested enough to sponsor this if it provides useful information.
It's not cheap.
Check out ENC labs:
www.enclabs.com