Ok, so last year I sowed my precious NT utric seeds in 1:1 peat/sand. I soon found my pots covered in the standard slime mold that always takes over my soils!
The problem is obviously substrate purity.
A German grower who was coaching me along mentioned that European growers use certain GRADES of peat and sand that is "totally limefree, sharp and open, and of a constant grain (I use 1mm sand), not a mix of too many different grain sizes."
He suggested that it wold be a good idea to use "H1 grade peat, and not more decomposed than H5 grade".
I'm really clueless about where I might find some H1 grade peat as he suggested.
It would be useful to know where to find these substrates because the "substrate stays clean for months (or even years) if you flush it with pure (distilled) water about weekly".
Any suggestions and comments appreciated!