You can wait till you do a water change but how much % we talking in a water change?
Red Sea's Reef Care program says to get good green / yellow coloration in corals, iron should be maintained at 0.15ppm. NSW iron is much lower... I read 0.0034.
http://www.seafriend...no/seawater.htm
I used to dose iron at around 5 ppb per week in SPS tanks.
I have a sneaking suspicion that it is a limiting nutrient that is important in keeping
Acropora palmata in captivity (there are only a couple people in the world who have success keeping this coral more than a year or so).
0.15 ppm is so ridiculously incorrect it's not even funny.
Iron is measured in the parts per
trillion range in surface seawater.
There is really no point in trying to test it with hobby test kits.
It is far too low in concentration to be detected without super fancy tools.
As
@Randy Holmes-Farley states in the AA article, there really is no harm in adding moderate amounts of it to your tank and observing your animals. Some people have reported good results in paled out Montipora recovering with Fe and Mn additions.
FWIW you need to add it chelated to something.
I use the recipe of sodium citrate and ferrous sulfate that Randy recommends.
You can also buy it in a bottle from Julian at Two Little Fishies.
