Hi all,
I read iron tests are not accurate how are getting your readings for iron ppm Zeus or is there a mathematical matrix solution?
You know how much iron (in ppm = mg/L) you've added from the percentage of iron in the compound (6% for FeEDDHA), how many grams you've added and the volume of the aquarium. You can use one of the <"
online calculators">, if you aren't confident about your calculations.
The availability of a nutrient depends on it staying in solution as ions, plants can only take up nutrients as ions from solution. Some compounds are always soluble, so when you add potassium nitrate (KNO3) you know that all the K+ and NO3- ions you've added are in solution and available to the plant, but it isn't like that with iron (or phosphorus (P)) compounds, most of them are insoluble.
So basically you can add as much iron chloride (FeCl3.6H2O) as you like, but it doesn't supply much plant available iron, because as soon as it dissolves the Fe+++ ions will find other anions (PO4---, OH-, HCO3- etc.) in solution and precipitate out as solid compounds, which are unavailable to the plant. The plant only has a very brief window of opportunity before the iron ionbs are mopped up and become solid precipitates.
When we use a chelator, like EDTA or EDDHA, the iron is bound in a complex organic acid, which means that it is unavailable to form other compounds, and also unavailable to the plant. If we keep the chelator in the dark this is how things remain, but FEEDTA is degraded by light which allows a trickle of iron ions (Fe+++) to be released into the aquarium.
cheers Darrel