Good point ,IR...

The same caution (awareness) should be used for any pre-packaged soil mix. Finding a happy balance is not rocket science, but is part of the challenge of getting used to ANY of the techniques we utilize for cannabis growing. If paying attention to what you are doing, (a personal grow diary and measuring spoons help bunches) it shouldn't take long to zero-in on what nute ratios work with what's in your soil.

If worried about overferting youngsters with pre-ferted Scotts, Supersoil or MG, try rinsing (flushing) soil prior to use.