plebian
Fish Crazy
I have a lightly planted aquarium and began supplementing iron. When researching iron supplementation I found that Seachem Flourish Iron was widely recommended by planted aquarium enthusiasts. Fortunately (or unfortunately), I also came across numerous reports that pH apparently plays a major role with respect to iron solubility. The one common thread found on this topic was that in the presence of oxygen, iron precipitates out of solution in all but the most acidic conditions. The recommended solution for this was to use chelated iron.
Clearly, additional research was required. What I found was the following commonly reported characteristics of various iron chelates at various pH levels:
Fe-gluconate begins to precipitate out of solution at pH > 4.5
Fe-EDTA begins to precipitate out of solution at pH > 6.5
Fe-DTPA begins to precipitate out of solution at pH > 7.5
Fe-EDDHA is stable at pH < 9.0
Assuming this information is correct, then Seachem Flourish Iron, which is Fe-gluconate, would be all but totally useless as an iron supplement in the vast majority of circumstances. Why then the popularity?
Additional research revealed that both the rate at which precipitation occurs, and the total amount of precipitate varies, across a range of pH values. Even so, most reports state that once a chelate reaches the point of initial precipitation, additional precipitation at a higher pH begins to occur very rapidly. Given this information, since the pH in my aquarium varies between 7.5 and 8.0, I decided that Seachem Flourish Iron and Fe-EDTA would be all but useless.
I began an experiment using Fe-DTPA to determine just how quickly, and how much, iron precipitate would form in my situation. I dissolved one gram in a glass of water (12 oz). This gave the water a deep amber color while maintaining perfect clarity. The first time I performed this experiment the pH measured 7.5. I left the glass of water sit for 4 days and observed no precipitation whatsoever. The color and clarity of the water remained exactly as it did when I made the solution. I repeated this experiment when the pH measured 8.0 with exactly the same result.
To say these results were surprising would be an understatement.
I am now conducting an experiment with a commercial product specifically promoted as an iron supplement, with the addition of several other micronutrients. The exact chemical ingredients are not labeled, but I believe the iron chelate being used in this formulation to be Fe-EDTA for a number of reasons. Following the dosage recommendations for a 150 gallon aquarium, I dissolved a capful of solution into a glass of water with a pH of 7.7. This changed the color of the water to a light yellow with perfect clarity. After 48 hours there is no change in color or clarity and no sign of precipitation.
Something is clearly missing from all the research I've done, including not simply planted aquarium forums, but chemical companies and scientfic articles on water chemistry.
NOTE: I measured pH using three different methods and each method produced very similar results, with a variance of less than 3%.
Clearly, additional research was required. What I found was the following commonly reported characteristics of various iron chelates at various pH levels:
Fe-gluconate begins to precipitate out of solution at pH > 4.5
Fe-EDTA begins to precipitate out of solution at pH > 6.5
Fe-DTPA begins to precipitate out of solution at pH > 7.5
Fe-EDDHA is stable at pH < 9.0
Assuming this information is correct, then Seachem Flourish Iron, which is Fe-gluconate, would be all but totally useless as an iron supplement in the vast majority of circumstances. Why then the popularity?
Additional research revealed that both the rate at which precipitation occurs, and the total amount of precipitate varies, across a range of pH values. Even so, most reports state that once a chelate reaches the point of initial precipitation, additional precipitation at a higher pH begins to occur very rapidly. Given this information, since the pH in my aquarium varies between 7.5 and 8.0, I decided that Seachem Flourish Iron and Fe-EDTA would be all but useless.
I began an experiment using Fe-DTPA to determine just how quickly, and how much, iron precipitate would form in my situation. I dissolved one gram in a glass of water (12 oz). This gave the water a deep amber color while maintaining perfect clarity. The first time I performed this experiment the pH measured 7.5. I left the glass of water sit for 4 days and observed no precipitation whatsoever. The color and clarity of the water remained exactly as it did when I made the solution. I repeated this experiment when the pH measured 8.0 with exactly the same result.
To say these results were surprising would be an understatement.
I am now conducting an experiment with a commercial product specifically promoted as an iron supplement, with the addition of several other micronutrients. The exact chemical ingredients are not labeled, but I believe the iron chelate being used in this formulation to be Fe-EDTA for a number of reasons. Following the dosage recommendations for a 150 gallon aquarium, I dissolved a capful of solution into a glass of water with a pH of 7.7. This changed the color of the water to a light yellow with perfect clarity. After 48 hours there is no change in color or clarity and no sign of precipitation.
Something is clearly missing from all the research I've done, including not simply planted aquarium forums, but chemical companies and scientfic articles on water chemistry.
NOTE: I measured pH using three different methods and each method produced very similar results, with a variance of less than 3%.
