Originally Posted by Seattle_Aquarist
I depends on what your target Fe ppm level is. I just recently removed some of the Iron Chelate I was dosing from my dosing schedule and added gluconate to replace it. I can't locate the post by Tom Barr but if I recall correctly he uses a mixture of CSM+B, ferrous gluconate; and a small amount of EDDHA.
I regularly have to remind myself that there is no "perfect" level for any of the nutrients I dose; each species I keep evolved a in different environment and what may be good for one is likely not ideal for another. I just strive to provide enough of each nutrient so the majority of my plants are growing well - sometimes I fail miserably!
Just a side note, EDDHA will last pretty much forever, or however long it takes for the plants to uptake it. Very stable chelate in a wide range of PH. But it is almost like blood red food coloring, dosing anymore than 0.05ppm to the tank and you will get a slight pink tint to the water. My dosing solution has 200ppm of EDDHA, and it is a very opaque dark red color. Mixing EDDHA Fe with some water and a tad of Vegetable glycerin for thickness would make some cinema quality fake blood!
Also as Zorfox said, we don't really know what the chelates do in the aquarium, so I'm very lean on the EDDHA at 0.01ppm per day. I'm trying to source some Ferrous gluconate as I dose everyday anyways, and it seems like a better approach so you don't get accumulation of chelates.
And I think Barr uses DTPA, with a ratio of 3-1-1 CSM+B, Ferrous Gluconate and DPTA if he hasn't changed his Micro recipe recently.
I had some issues which seem to relate to the CSM+B (toxicity) but I can't say for sure what it is in the CSM+B that causes it, but AR minis would twist like crazy and melt away at EI levels for me.
And looking at Burr740 journal, it would seem like plants need very little of CSM+B, it's called Trace elements for a reason. So I would rather go 1-3-1 CSM+b, Ferrous gluconate and DTPA. Skip the DTPA all together if you dose every day.
But thats just my personal view on the topic.