Is this the stuff?

Sunshine Mix #4 - 3.8 cf compressed

If so...it's a peat based product, and the optimal range for water ph in this medium is, as previously stated, 6.3 to 6.8. I'd aim for the 6.7 to 6.8 range, myself. (adding nutes lowers it further anyway) Although it's not "soil", it's refered to as a potting soil. Most potting soils are peat-based.

The numbers you quote are more for coco or hydro, aren't they? I don't play with hydro, so I'm not at all sure about that. What I am sure of is that 5.7 to 6.2 ph is way too low for the above Sunshine Mix #4.

Also, as the dolomitic limestone in your potting soil degrades over time and use, the ph can eventually take a dive. (adding to an already existing low ph problem)

If that's not it, a link to the proper medium would help, as I must be confused. :thumbsup: