I think it is funny that people are so scared to put trace elements into their tank without testing each element. Do you test each element of the Salt water you do changes with -- NO
! Also, if stability is a factor in the health of a tank, then water changes are actually a bad thing. I understand that people think water changes will remove wastes and metals and all the other bad stuff, but the truth is that unless you are doing massive water changes, you cannot effect the water chemisty very much. Thnik about it, if you did 50% water changes, and your Nitrates were at 20, then the best you could get would be 10 nitrates, but that is also assuming the nitrates are always equally distributed in the water. (Which they are not!) And as for the trace elements, you would only be putting half of the initial amount back in, so you could actually still be deficient in the available trace elements.
If you cannot tell, I am an advocate of watching your parameters and doing changes when there is a real reason. If my filtration is working right, I do not do anything but top off and add trace elements, but then again I am usually on the minority side of ideologies anyhow.