I'm sure there is an old thread covering this question, but I finally gave up...

I have a new 50G high (36x15x21) tank, using EI with TMG (10ml 3x per week), 96w CF lighting, and have ADA Aqua Soil as my substrate...

Question: Do I need to dose iron?

If so, (from an old thread) I will plan on getting Iron Chelate (10%) and placing 2.5g in 1000ml distilled water (or RO?) and dosing 15 mls 3x per week. If I was not dosing with TMG, I would use 5g, instead of 2.5g. If there is a better or easier way, please let me know.

If ADA Aqua Soil has iron in it and I do not need to dose iron at this time, when does the ADA AS iron run out? Should I start dosing iron in a year or something like that?

TMG has Fe in it already.
You do not need to dose more, you can if you wish, but it's not needed.
ADA As has it as well.
So you are covered.

Regards,
Tom Barr