Thank you Josh. Let me read those posts tonight. I was thinking of getting the following starter kit in terms of EI: https://www.aquariumplantfood.co.uk/fertilisers/dry-chemicals/starter-kits/ei-starter-kit.html
I watched a George Farmer review of the product and it seems to be recommended by a few other aquascapers.
That one looks good!
I couldn't find out what chelate is used - but this blurb:
Can I dose Macro & Micro mixes on the same day?
No, the Iron (Fe) in the Chelated Trace and the Phosphate in Potassium Phosphate (KH2PO4) have a tendency to react with each other, especially at higher pH rendering them un available to the plants as it forms Iron Phosphate.
Suggests that it is EDTA/DTPA and my guess is EDTA. Here is the chelate chart of relative concentration at pH.
But again, there is a thought that you can just dose more EDTA or whatever (as long as your pH isn't extremely extremely high), instead of picking a "more suitable" chelate - and others say that should pick the "most suitable" chelate. I don't have enough experience with both approaches to comment. Just note that if you have excess EDTA and the pH increases the chelate will break off and then will bond with something (likely phosphates) as a result, reducing your overall phosphate (if that was what it bonded to) availability- so you would need to adapt your dosing regime to suit it. But these are details.
Just get that one and let's see how it goes.