Hi guys,
Just found this thread and thought I’d add my views. We grow around 400 tomato plants a year using Fertile Fibre seed compost and then transplanting into Fertile Fibre potting compost. We sow with bottom heat and use a mist bench to raise the seedlings. Yellowing rarely happens before we pot on from modules into 9cm pots. We usually get near 100% germination and the plants stay in 9cm until point of sale.
The commonest problem with using Fertile Fibre is that people use it straight out of the bag. It must be well fluffed up before use and not compacted subsequently. Also heavy watering can cause a crust to form (particularly with the seed compost), so go easy as overwatering Fertile Fibre is another common problem.
We use Fertile Fibre extensively and bar one problem batch (see my reply to that thread) have had no problems in more than eight years. Because of those problems we trialled Fertile Fibre against Com Vert this year. See pictures at http://www.gwynfor.co.uk/composts.html for the results of this trial.