Hi and thanks for all your comments, I'm getting somewhere here...
As that indicates problems are most likely to come with <"
iron availability">.
So, just in case this is an issue, I may as well add extra cheated iron from APFUK...?
A practical approach may be to dose "Full EI" and use @dw1305s duckweed index to determine the amount of Ca and Mg (and maybe potassium) that you need to add (this would be in the form of DIY salts or GH booster). Maybe omit the KH part though
This is edging into a-bit-complicated-for-me territory, but as I understand it the duckweed index is the use of floating plants to expose any deficiencies, having excluded co2 and light, as they are abundant at the surface...? I'm not sure I would know what the hell to do if I did see an issue, as I wouldn't know what I was deficient in! The word duck weed sends a shiver down my spine but I assume other, more attractive, less invasive floating plants would serve the same purpose? I'm putting this in the maybe something soon category for now - thank you.
If using 100% RO water I would advise EI dosing with root tabs which should cover all the nutrients your plants need.
Hard water is tricker for the reasons Darrel mentioned 😉
I'm 100% tap water, (although I am filtering out Nitrate and Phosphate, as I believe they are excessive in my water, I also run an unplanted cichlid tank plus it gives me a more stable starting point to work from, also my planted tank is quite heavily stocked and nitrates could otherwise run away... My nitrate was about 40ppm at water change day last week as it is...) In any case, I'm tap all the way.
So, in conclusion (for now) maybe I should aim for a combination of the APFUK and Clive methods listed in the chart Zeus posted here. That is to say APFUK nitrate level and Clive everything else... plus cheated iron supliment.
Does this sound like a logical safe starting point to work from?