[AQTCJAK]

This is from the Hagen master Test Kit on Iron

First, Toxic, non-chelated (free) iron needs to be distiguished from the less dangerous chelated form of iron. Non-chelated iron iron can be toxic at levels of 0.3 mg/L and above. Second, iron plant supplements need to be monitored to ensure safe levels. In salt water, ensure that the level of iron does not reach a detectable reading. Natural ocean water contains an average of 0.001 mg/L

So it is possible you might have iron levels above that that