Sound like some Fe DTPA or Fe EDDHA is needed as @dw1305 surgested and unstable [CO2] will not help
The Easy-Life bottle just says Iron(II).
So, something like this https://aquaplantscare.uk/shop/aquatic-plants-fertiliser/organic-iron-fe-8-dtpa-chelated/ would work? Can I use it alongside the Tropica fertilizer?
Do you have an idea how high a concentration I should aim for?
Do you happen to know this seller (no reviews on Trustpilot)?
That's a lot of questions. Sorry.