I had spent a far bit of time on the net looking at using John Innes #2 and #3 for the substrate. I have a very low light tank (96 ltrs, 18W 6500K light), so went for #2 as it has less nutrients, covered with 4mm gravel. Tank been running for 3 weeks now, Ammonia has just dropped to 0.25, nitrite still very high (+5ppm).
Yesterday I have discovered this site, and read a lot of posts saying don't use #2, use #3. Now I'm hoping I have made the correct choice. My Bacopa Australis has grown about 3 inches. my java fern and Rotala Rotundifolia have also grown a little. The Crypocoryne Wendtii is look good, so does the Anubias Barteri Nana.
I will update this post in a few weeks.