Trace elements and tap water
It seems that balancing trace elements can be a tricky business.
I have read that too much of one element can interfere with a plant's
ability to take up another. I know that tap water usually has higher
concentrations of dissolved metals than is found in nature. I also
know that trace elements are usable by plants only in certain forms
(chelated). All these facts lead to a confusing situation: even if I
get an iron test, how do I know what part of the iron is in usable
form? Does an excess of unchelated iron cause problems with other
trace elements? What is the best way to remove excess elements (ie
iron and copper) from tap water? I was told by someone at a fish
store that you can remove dissolved metals with a polyfilter, and
that you can tell what is being removed by looking at the color of
the filter after it runs for a while (green => copper, red => iron)
but I don't know how reliable this advice is. My polyfilter does
show a definite reddish tinge after a day or so. I tend towards red
algae problems even with regular (weekly 20%) water changes. I use
dupla drops, good lighting, undergravel heater, etc. and my nitrates
are barely registering. Just an idle thought: does the red pigment
in red algae indicate some affinity between it and high iron content?
Anyway, my highschool chemistry hasn't equipped me to deal with these
issues, and I can't believe that dupla drops or any other trace
element additive will fit all situations equally well.