Wow, I thought I had pretty good luck with it.
Interesting, our water is high in calcium and I use Miracle Gro and fish Emulsion both of which contain Magnesium. Our soils here are naturally high in Magnesium to the point that Epsom salts are generally not recommended. Our soils are deficient in Manganese.
Quite interesting Hanry!!
For three years now I used a coir / enriched peat mix for sowing. Not coir dust but short cut fibers. Aim being a longer lasting media texture. Had very good results for two years and this last one I got high persisting chlorosis.
This information is quite welcome even if I cannot choose the coir brand I buy nor know its origin…
Now I know what to try.